On the June 30, 2009 episode of ECW, Sheamus made his unannounced debut as a villain, quickly defeating a local competitor. Sheamus soon entered into a critically well-received rivalry with Goldust after defeating him on 29 July. After exchanging victories in the following weeks the two appeared on the Abraham Washington Show talk segment, leading to a No Disqualification match on 1 September which was won by Sheamus. Sheamus then began a feud with Shelton Benjamin which was hot-shot into a deciding match on 27 October which Sheamus won.
His rivalry with Benjamin ended prematurely because Sheamus had already been moved to the Raw brand. He made his Raw debut by defeating Jamie Noble on 26 October. In the following weeks, he continued to attack Noble causing him to retire, and, in lieu of competition, assaulted the timekeeper and commentator Jerry Lawler on 16 November at Madison Square Garden. The following week Sheamus appeared on his first WWE pay-per-view event, Survivor Series. Sheamus appeared as part of The Miz's team in a traditional five-on-five elimination tag team match. He eliminated fellow Irishman Finlay and made the final pinfall to eliminate the opposing captain John Morrison and survive along with The Miz and Drew McIntyre.
The following night on Raw, Sheamus won a "break-through" battle royal for wrestlers who had never won a world championship, to become the number one contender to John Cena's WWE Championship. At the contract signing immediately afterwards, Sheamus put Cena through the table, and the Raw guest host, Jesse Ventura, announced it would be a Table match. On 13 December at TLC: Tables, Ladders & Chairs pay-per-view, Sheamus defeated Cena to win the WWE Championship, his first championship in WWE, making him the first Irish-born WWE Champion. The following night on Raw, Sheamus was awarded the 2009 Breakout Superstar of the Year Slammy Award. On 31 January 2010, at the Royal Rumble, Sheamus defeated Randy Orton by disqualification to retain the WWE Championship, following interference from Orton's tag team partner Cody Rhodes. On 21 February, Sheamus lost the WWE Championship at the Elimination Chamber pay-per-view in the Elimination Chamber match after he was eliminated by Triple H. During the match, Sheamus suffered a concussion and as a result did not attend Raw the following night. Upon his return, he took revenge on Triple H with an attack to set up a match at WrestleMania XXVI that Sheamus lost. The following month at Extreme Rules, Sheamus attacked Triple H at the beginning of the show and later defeated him in a Street Fight. After a series of kicks to the head to win, he continued his assault after the match finished resulting in Triple H being written off television for ten months.
On June 20 at Fatal 4-Way pay-per-view, Sheamus won a fatal four way match, following interference from The Nexus that allowed him to pin John Cena, thus winning the WWE Championship, and beginning his second WWE Championship reign. He went on to defeat Cena a third time in a steel cage match to retain the championship on 18 July at the Money in the Bank pay-per-view, and against Randy Orton on 15 August at SummerSlam, which ended in disqualification, meaning that Sheamus retained his title. On 19 September at Night of Champions, Sheamus lost the WWE Championship to Randy Orton in a Six-Pack Elimination Challenge, which also included Chris Jericho, Edge, John Cena, and Wade Barrett. Sheamus received his rematch for the title on 3 October at Hell in a Cell, but was again defeated by Orton in a Hell in a Cell match.
He bounced back on 29 November, with wins over Kofi Kingston and John Morrison to become King of the Ring, after receiving a bye through the second round. As King Sheamus, he faced Morrison again at the TLC: Tables, Ladders and Chairs PPV for a future WWE Championship match but lost the Ladder match. Going into 2011, he continued to lose to Morrison in a mixture of singles and tag team matches. Triple H returned on 28 February and took revenge for his scripted ten-month injury by putting him through the announce table. Right after that, Sheamus was defeated by Evan Bourne who returned to Raw after a four-month injury. On 7 March, after losing a match against Daniel Bryan, Sheamus challenged him to a rematch with his WWE career on the line against Bryan's United States Championship. He won his match against Bryan the following week, winning his first United States Title. The rematch between Sheamus and Bryan took place on 3 April, during the preshow of WrestleMania XXVII, and ended in a draw after interference from the lumberjacks. The next night on Raw, Sheamus retained the United States Championship against Bryan in a rematch. After the match, the debuting Sin Cara saved Bryan from an attack by Sheamus.
In the 2011 Supplemental Draft, Sheamus was drafted to the SmackDown brand. Sheamus made his SmackDown debut on the 29 April episode, attacking Kofi Kingston. Although he took the United States Championship with him, he lost it back to the Raw brand at Extreme Rules when Kingston defeated him in a tables match.
On the June 3 episode of SmackDown, Sheamus lost a World Heavyweight Championship match to Randy Orton due to biased refereeing from Christian, beginning a turn from a villainous character to a fan favorite over the following weeks. Two weeks later, he lost a match to Christian, blowing his chance to compete in the World Heavyweight Championship match at WWE Capitol Punishment. Afterward, he was punted by Randy Orton. Sheamus' face turn culminated in him attacking Mark Henry for being a bully, though he lost to him by count-out at SummerSlam. After this loss, Sheamus went on a 14 match winning streak that ended after outside interference from Christian, with whom he had been feuding. During this time, Sheamus defeated Christian in three consecutive matches at Hell in a Cell, Vengeance, and on Smackdown.
He then went on a 12 match winning streak building towards winning the 2012 Royal Rumble. He entered the match twenty-second and won by last eliminating Chris Jericho to earn a main event championship match at WrestleMania XXVIII.
On 19 February, at Elimination Chamber, Sheamus attacked World Heavyweight Champion Daniel Bryan after the latter retained his title in the Elimination Chamber match, indicating he would face Bryan at WrestleMania. On 1 April, at WrestleMania XXVIII, Sheamus defeated Bryan in a record eighteen seconds to win his first World Heavyweight Championship. On the following episode of Smackdown, Sheamus was defeated by Alberto Del Rio via disqualification, thus earning Del Rio a future title match. On 29 April at Extreme Rules, Sheamus successfully defended the World Heavyweight Championship against Bryan in a two out of three falls match. On 20 May at Over the Limit, Sheamus defeated Alberto Del Rio, Chris Jericho, and Randy Orton in a fatal-four-way match to retain the World Heavyweight Championship. On 17 June at No Way Out, Sheamus defeated Dolph Ziggler to again retain the World Heavyweight Championship. On the 29 June episode of SmackDown, Sheamus successfully defended the World Heavyweight Championship against Ziggler and Alberto Del Rio in a triple threat match. On 15 July at Money in the Bank, Sheamus defeated Del Rio to retain the World Heavyweight Championship. On the July 27 episode of SmackDown, Del Rio defeated Daniel Bryan, Kane, and Rey Mysterio in a four-way match to again become number one contender for the World Heavyweight Championship. The title match, originally announced for SummerSlam, was moved to the 10 August episode of SmackDown, after Del Rio threatened to press charges against Sheamus for stealing his car on the previous episode of Raw, which would have prevented Sheamus from appearing at SummerSlam. However, before the match began, Del Rio and men posing as police officers attacked Sheamus. This led to SmackDown General Manager Booker T taking away his number one contender status. However, the following week, Sheamus had the title match put back on for SummerSlam. At the pay-per-view on 19 August, Sheamus defeated Del Rio once again to retain World Heavyweight Championship. On the 7 September episode of SmackDown, Booker T reluctantly granted Del Rio's request to ban the Brogue Kick, after Sheamus knocked out his ring announcer Ricardo Rodriguez with the move on the previous Raw. After Sheamus hit David Otunga with the Brogue Kick three days later on Raw, Booker T announced that if Sheamus used the move again he would be stripped of the World Heavyweight Championship. However, on 16 September at Night of Champions, Booker T announced that he had concluded his investigation into the dangers of the move and uplifted the ban. In the match that followed, Sheamus used the Brogue Kick to defeat Del Rio and retain the World Heavyweight Championship. On 28 October at Hell in a Cell, Sheamus lost the World Heavyweight Championship to Big Show, ending his reign at 210 days. Sheamus defeated Show by disqualification on 18 November at Survivor Series, so did not win the title. Afterward, Sheamus repeatedly hit Show with a steel chair. This led to a Chairs match on 16 December at TLC: Tables, Ladders & Chairs, where Sheamus failed again to regain the World Heavyweight Championship. On the 24 December episode of Raw, Sheamus defeated Show in a non-title lumberjack match.
On 27 January 2013, at the Royal Rumble, Sheamus entered the Royal Rumble at number eleven and eliminated five other competitors before being the twenty-eighth man eliminated by Ryback. After being a frequent target of The Shield, Sheamus gained vengeance on the stable when he united with John Cena and Ryback to attack them. This culminated in a six-man tag team match on February 17 at Elimination Chamber, where the Shield emerged victorious. The following night on Raw, Sheamus and Ryback teamed up with Chris Jericho to face The Shield in a rematch, but were again defeated. In late February, Sheamus aligned himself with Randy Orton to feud with the Shield. Over the next weeks, Sheamus and Orton saved each other from attacks by The Shield and Big Show. On the March 15 episode of SmackDown, Sheamus and Orton were then allowed to pick a third partner to face the Shield in a six-man tag team match at WrestleMania 29 and chose Ryback. Three days later on Raw, however, Ryback was booked for another match at the event, leaving the spot open. Later that night, Big Show saved the two from an attack by The Shield and was immediately recruited as their partner. On 7 April at WrestleMania 29, Sheamus, Orton and Show were defeated by The Shield, after which, both men were knocked out by Show. The following night on Raw, Sheamus and Orton faced off in a match to earn a match with Big Show, however, the match ended in a no contest after Show interfered. Sheamus and Orton then teamed up to defeat Show in two handicap matches, first on the April 12 episode of SmackDown via cont-out, and second on the April 15 episode of Raw via pinfall. At the same time, Sheamus reignited a feud with Mark Henry, after the two repeatedly attacked each other backstage. On the April 19 episode of SmackDown, Sheamus and Orton were defeated by Big Show and Mark Henry in a tag team match. With Orton and Show out of the picture, Sheamus would continue to feud with Henry as the two started testing each other's strength. Their rivalry built to a strap match on 19 May at Extreme Rules, where Sheamus emerged victorious. Sheamus then began feuding with Damien Sandow, when Sandow hosted a series of mental challenges on SmackDown, and Sheamus repeatedly interrupted and tried to solve the challenges. However, when Sheamus failed to solve the puzzles, he instead resorted to physical violence with the Brogue Kick. On June 16, during the Payback pre-show, Sheamus defeated Sandow in a singles match. The following night on Raw, Sheamus was defeated by Sandow and Cody Rhodes in a handicap match after Sandow pinned him with a roll-up. The rivalry culminated in a Dublin Street Fight on the June 28 episode of SmackDown, where Sheamus emerged victorious. On July 14 at Money in the Bank, Sheamus competed in the WWE Championship Money in the Bank ladder match, but was unsuccessful as the match was won by Randy Orton. During the match, Sheamus suffered a hematoma on his left thigh after being thrown into a horizontal ladder, which prevented him from competing that week. Sheamus returned to in-ring action on the July 22 episode of Raw, losing to World Heavyweight Champion Alberto Del Rio in a non-title match. On August 7, WWE.com confirmed that Sheamus had suffered a torn labrum in his shoulder that will require surgery, and would miss up to four-six months of ring action.
On 26 January at the Royal Rumble event, Sheamus returned to the Royal Rumble Match, as a surprise entrant, entering at number 17, where he eliminated Big E Langston in the match, but later on was eliminated by Roman Reigns in the final three between him, Batista, and Reigns. The next night on Raw while Daniel Bryan was about to get attacked by The Shield in the opening of the show, Sheamus and John Cena made the save, which resulted in the main event being a 6 man tag team qualification match for the Elimination Chamber in February to compete for the WWE World Heavyweight Championship. Later on in the night Sheamus, Daniel Bryan and John Cena won by disqualification and qualified to be in the Elimination Chamber, because The Wyatt Family interfered in the match. On the January 31st episode of Smackdown, Sheamus teamed with Daniel Bryan, and Rey Mysterio against The Shield in a losing effort. He then began a brief feud with Christian by facing him on Raw and SmackDown on multiple occasions leading up to WrestleMania, with each time Sheamus coming out on top. He was a part of the WrestleMania XXX Andre The Giant Memorial Battle Royal where he made it to the final four before he and Alberto Del Rio eliminated each other. On April 14, Sheamus participated in the Intercontinental Championship #1 Contender Tournament, which was held on Raw. He saw himself advancing to the next round by defeating Jack Swagger, before losing to Bad News Barrett in semi final on April 21 edition of Raw. On the May 5 episode of Raw Sheamus would win a 20-man battle royal to win the United States Championship for the second time, last eliminating previous champion Dean Ambrose. Sheamus then began feuding with Cesaro and his manager Paul Heyman, culminating in a match between Sheamus and Cesaro for the US Championship at Payback, which Sheamus won. On June 9th, Sheamus defeated Bad News Barrett to qualify for the Money in the Bank ladder match for the vacant WWE World Heavyweight Championship. The match was won by John Cena. Sheamus was in the Intercontinental Championship Battle Royal at Batttleground, but lost. The match was won by The Miz. At Night of Champions, Sheamus successfully defended the title against Cesaro and retained the championship against The Miz at Hell in a Cell. Sheamus would lose the United States Championship on the WWE Network to Rusev on the November 3 episode of Raw, ending his reign at 182 days. Sheamus was due to be on John Cena's team at Survivor Series, but he was attacked by Rusev and Mark Henry in the course of a match with Big Show, resulting in Sheamus being (kayfabe) seriously injured after receiving a World's Strongest Slam through an announce table. On the February 9th edition of Raw it was announced that Sheamus would be returning soon.
He returned on the 30 March episode of Raw, debuting a new look of a mohawk and braided beard, and attacked Dolph Ziggler and Daniel Bryan, turning heel. On the 16 April episode of SmackDown, Sheamus announced that he would face Ziggler in a Kiss Me Arse match at Extreme Rules, which he lost. However, he refused to follow the stipulation, and instead made Dolph Ziggler kiss his 'arse'. At Payback, Sheamus defeated Ziggler in a rematch. At Elimination Chamber, Sheamus was defeated by Ryback after making it to the final two, therefore not winning the Intercontinental Championship. At Money in the Bank, Sheamus won the Money in the Bank ladder match to earn a WWE World Heavyweight Championship contract. Sheamus then began a feud with Randy Orton, losing to Orton at Battleground, but defeating Orton at SummerSlam.
At Survivor Series, Sheamus cashed in his Money in the Bank contract and defeated newly crowned champion Roman Reigns, after he refused to shake hands Triple H, to win the WWE World Heavyweight Championship, thus aligning with Triple H and The Authority. On the November 30 edition of Raw, Sheamus announced that he had formed his own stable called the League of Nations (featuring King Barrett, Alberto Del Rio, and Rusev). This new stable - with the theme of all members having been born and becoming stars overseas - remained associated with the Authority, while becoming its own entity. In addition, he proclaimed his championship reign as "Sheamus 5:15", which is a play on Austin 3:16 and Reigns' short-lived tenure as champion for five minutes and 15 seconds. At TLC, with the help of his fellow League of Nations members, Sheamus retained the WWE World Heavyweight Title against Reigns in a TLC match. After the match, Reigns snapped and viciously attacked Sheamus as well as Triple H. This resulted in a rematch the following night on Raw for the title with the added stipulation that Reigns would be fired should he lose. Despite interference from chairman Vince McMahon, Sheamus lost the championship, ending his reign at 22 days. On the January 4, 2016 episode of Raw, he failed to regain the title from Reigns with McMahon as special guest referee. On January 8, at a live event in Houston, Sheamus lost to Brock Lesnar. On January 28, Sheamus received an injury to his arm that was later announced to be tendonitis.
Sheamus returned on the February 15 Raw, teaming with Rusev and Del Rio to defeat The Lucha Dragons and Neville. At Fastlane, WWE Tag Team Champions The New Day began mocking The League of Nations, calling them the "league of booty". They then continued to mock The League of Nations in various segments and skits while simultaneously feuding with other teams. At Roadblock, Sheamus and Barrett challenged for the WWE Tag Team Championship, but were unsuccessful. The following night on Raw, The New Day defeated Del Rio and Rusev, prompting all four members of The League to attack The New Day after the match. The League of Nations then challenged The New Day to a match at WrestleMania 32, where they defeated The New Day. After the match, they were confronted and attacked by Mick Foley, Stone Cold Steve Austin, and Shawn Michaels.
On the April 4 episode of Raw, Barrett and Sheamus faced The New Day in another tag team title match, in a losing effort. After the match, the League of Nations blamed Barrett for being the "weak link" and attacked him, ejecting him from the group, before the rest of the team was attacked by The Wyatt Family. The feud was suspended within a month due to Bray Wyatt suffering an injury.
On the April 28 episode of SmackDown, The League would compete in a six-man tag match against Sami Zayn, Kalisto and Cesaro, however, Del Rio and Rusev walked out during the match. Sheamus, who would do the same, confronted Del Rio and Rusev during a brawl, and said that the league is finished, confirming the end of the group. Del Rio would also confirm in an interview that the group was finished.
On the May 2 episode of Raw all three members of the former stable competed in the United States Championship number one contender match. Rusev won the match, and eliminated both Sheamus and Del Rio. On the May 23 episode of Raw, Sami Zayn defeated Sheamus to qualify for the Money in the Bank ladder match at the Money in the Bank pay-per-view. At the Money in the Bank pay-per-view, Sheamus suffered a loss to Apollo Crews.
On July 19, at the 2016 WWE draft, Sheamus was drafted to Raw. On the July 25 episode of Raw Sheamus was part of a fatal four way match to determine the number one contender for the newly unveiled WWE Universal Championship; the match was later won by Roman Reigns. Sheamus would then be embroiled in a rivalry with Cesaro, after losing to Cesaro on the August 1 episode of Raw the two would continue to brawl after the match with match officials having to pull them apart. On the August 8 episode of Raw, after losing to Cesaro in a rematch, he would later cost Cesaro the United States Championship after interfering in his main event impromptu match against Rusev. The following week, Raw General Manager Mick Foley booked Sheamus and Cesaro in a Best of Seven Series, with the first match taking place at SummerSlam, which Sheamus won. Sheamus would defeat Cesaro in the second and third matches, but lost to Cesaro in the fourth, fifth and sixth matches. At Clash of Champions, neither man won as the match was declared a no contest. The next night on Raw, to help prevent a disaster with their health, Mick Foley decided to make the two partners to receive a future WWE Raw Tag Team Championship opportunity. Later that night, they defeated a few local athletes, but still didn't seem to be seeing eye to eye.
On the November 7 episode of Raw, Cesaro and Sheamus were announced as part of Team Raw for the 10–on–10 Survivor Series Tag Team Elimination match at Survivor Series on November 20, 2016 which Team Raw won with Cesaro and Sheamus being the sole survivors of their team. The next night on Raw, Sheamus and Cesaro again failed to capture the tag titles from New Day, after failing at Hell in a Cell in October. On December 18 at Roadblock: End of the Line, Sheamus and Cesaro defeated The New Day to win the Raw Tag Team Championship, marking Sheamus' first tag team championship.