Dean appeared at house shows on December 16 and 17, 2011, losing to Daniel Bryan. On December 19, he lost to Ted DiBiase in a dark match prior to Raw. On March 4, 2012, Ambrose beat Drew McIntyre at a house show in Albany, Georgia, marking his first win in front of a main WWE crowd.
Ambrose made his main roster debut on November 18, 2012 at the Survivor Series pay-per-view alongside Roman Reigns and Seth Rollins, where they assaulted Ryback during the triple-threat main event for the WWE Championship, leading to CM Punk pinning John Cena to retain his title.
The trio declared themselves "The Shield" and vowed to rally against "injustice" while denying that they were working for Punk, but would routinely emerge from the crowd to attack Punk's adversaries such as Ryback, The Miz, Kane and Daniel Bryan, who had attempted to save Kane. This led to a Tables, Ladders, and Chairs match being set up for the TLC pay-per-view pitting the three men of the Shield against Ryback and Team Hell No (Kane and Bryan), which Ambrose, Reigns and Rollins won in their debut match. The Shield continued to aid Punk after TLC; during Punk and Ryback's TLC match for the WWE Championship on the January 7 episode of Raw, they attacked Ryback, which resulted in Punk retaining his title. During the Royal Rumble event where the Rock challenged for Punk's WWE Championship, match, a blackout occurred and the Rock was attacked in the darkness by unknown assailants, directly leading to Punk pinning Rock; the announcers blamed the Shield for the attack. The match was later restarted with Rock winning. The next day on Raw, the Shield attacked and laid out John Cena; Sheamus and Ryback suffered the same fate when they attempted to save Cena. Later in the show, it was revealed through footage played by Vince McMahon that Punk and/or his manager Paul Heyman had been paying the Shield and Brad Maddox to work for them all along. This set up a six-man tag team match at Elimination Chamber, which the Shield won. At WrestleMania 29, The Shield beat Randy Orton, Sheamus, and Big Show in a six-man tag-team match when Ambrose pinned Orton. On the April 22nd edition of Raw, the Shield defeated Team Hell No and The Undertaker in a six-man tag-team match. Ambrose wrestled his first singles match in the WWE on the April 26 edition of SmackDown, losing via submission to The Undertaker. However, immediately after the match Ambrose and the rest of the Shield would viciously attack Undertaker, beating him down with chairs and putting him through the announcers' table. On the April 29 episode of RAW, The Shield defeated Kane, Daniel Bryan and John Cena in a six-man tag team match. On the May 3 episode of SmackDown, Ambrose defeated Kane with a headlock driver.
On May 13 in an episode of RAW, The Shield suffered their first loss in a Six-Man Elimination Tag Team Match by disqualification when Rollins and Reigns (who were already eliminated) attacked John Cena while he was performing an STF submission hold on Dean Ambrose. On May 19 at Extreme Rules, Ambrose defeated Kofi Kingston to win the United States Championship, his first singles title in WWE. Later on that night, Rollins and Reigns defeated Team Hell No in a tag team tornado match to capture the WWE Tag Team Championships, thus giving all three members of The Shield championship gold. Ambrose made his first televised title defense on the following episode of SmackDown, losing to Kingston via disqualification after Reigns and Rollins interfered, but retaining the title as a result. The Shield would continue their assault on Kingston until Randy Orton and Sheamus made the save. Theodore Long then came out to set up a six-man tag team match that ended with Ambrose pinning Kingston for the win. Three days later on Raw, Ambrose defeated Kingston again to retain his title. At WWE Payback, Ambrose scored a countout victory over Kane to retain the United States Championship. On June 17, edition of RAW, he received a disqualification loss against Kane after Roman Reigns and Seth Rollins attacked Kane during the rematch for United States Championship. At Money in the Bank ppv Ambrose competed in the World Heavyweight Championship Money in the Bank ladder match, which he almost won with the help of Rollins and Reigns however he was unsuccessful in winning losing to Damien Sandow. Ambrose retained his United States Championship at Summerslam by disqualification when The Shield speared Rob Van Dam. Afterwards, Ambrose would begin a feud with Dolph Ziggler when Ziggler disagreed with Triple H's management of WWE. On September 15 during Night of Champions pay-per-view Ambrose successfully defended his title by defeating Ziggler. The following night on Raw, Ambrose would lose to Ziggler in a non-title match, which lead to another title defense later in the week on SmackDown, but Ambrose retained the championship when Reigns and Rollins interfered. On the October 16 Episode of Main Event, Ambrose defeated Ziggler to retain his United States title. Later that month, on October 27, at the WWE Hell in a Cell pay-per-view, in a title match, Ambrose was defeated by Big E Langston by count-out, therefore retaining his United States Championship. On December 15th at the TLC, the Shield would lose to Punk in a 3-on-1 Handicap match. Ambrose was accidentally speared by Roman Reigns allowing Punk to win the match.
On the 10 February 2014 episode of Raw, Ambrose's open challenge for his title was answered by Mark Henry, in which Ambrose only retained his title upon disqualification due to the Shield's interference; Reigns followed up by defeating Henry without interference on the next Raw. At the Elimination Chamber pay-per-view, the Shield lost to the Wyatt Family; during the match, Ambrose and Bray Wyatt brawled into the crowd, but Wyatt returned to the ring with no sign of Ambrose, which caused Rollins and Reigns to be outnumbered and overwhelmed. On the March 3 Raw, the Shield lost a rematch with the Wyatt Family when the Shield's poor teamwork led to Rollins walking out during the match; Rollins claimed that he had enough of being the glue holding the group together. However, The Shield quickly got back on the same page and began a feud with Kane, turning all members of The Shield faces in the process. During this feud, Kane was joined by the New Age Outlaws to battle The Shield in a six-man tag-team match at WrestleMania XXX, which The Shield won.
On Raw after WrestleMania, The Shield officially severed ties with The Authority when Kane revealed that Triple H had coordinated the attack on them several weeks prior. As a result, The Shield attacked the entire Authority, protecting new WWE World Heavyweight Champion Daniel Bryan, thus solidifying their face turn. The next week, Triple H placed The Shield in an 11-on-3 Handicap match; following the match, The Shield was attacked by a reunited Evolution.
On Monday April 28, 2014, Ambrose marked 344 days as U.S. Champion. This made him the longest reigning U.S. Champion under the WWE banner, surpassing Montel Vontavious Porter's previous record of 343 days set in 2007-2008. On May 4th Extreme Rules 2014 The Shield beat Evolution in a Six Man Tag Team Match. On May 5, after 351 days, Ambrose lost the title to Sheamus after being forced to defend it in a 20 man battle royal. He was the last wrestler eliminated. On the next SmackDown, Ambrose failed to regain the championship in a singles match against Sheamus. The Shield once again defeated Evolution at Payback. The next night, Batista left Evolution, prompting Triple H to initiate "Plan B" in his quest to destroy the Shield; this involved Rollins turning on Ambrose and Reigns, subsequently aligning himself with Triple H. The following week on Smackdown, Ambrose faced Bray Wyatt for a spot in the Money in the Bank match for the WWE World Heavyweight Championship, but lost due to a distraction from Rollins. As Ambrose and Reigns quietly separated, Ambrose debuted new ring attire and new entrance music. After being added to the Money in the Bank ladder match at Money in the Bank at Rollins' request, Ambrose lost the match when Kane attacked him to help Rollins win. Ambrose was scheduled to face Rollins at Battleground, but Ambrose was ejected from the arena by Triple H. Later that night, Rollins came out and announced that he had won their match by forfeit. Ambrose would then burst into the ring and attack Rollins and a vicious brawl ensued where both men had to be pulled apart by both The Authority and security. Rollins was then shown leaving the arena into the parking lot, where Ambrose was hiding in the trunk of a car and attempted to attack Rollins with a tire iron before Rollins managed to drive away. Ambrose and Rollins eventually fought at SummerSlam in a Lumberjack match, where Ambrose lost.
During an interview on the following Raw, Ambrose made Rollins the victim of a surprise Ice Bucket Challenge and beating. Triple H decided to have them fight in a SummerSlam rematch with the WWE Universe voting on the stipulation; the vote was made for a Falls Count Anywhere match. Ambrose was almost closing in on a victory when Kane (who had been sitting ringside) once again interfered and set up Ambrose for Rollins's Curb Stomp through a pile of concrete blocks next to the announce table. Rollins was given the win via knockout and Ambrose was stretchered out of the arena. Ambrose refused treatment and went missing shortly after. The storyline was put to place to allow Ambrose's absence on television in order to film Lockdown. He returned at Night of Champions on September 21, attacking Rollins. On the October 13 episode of Raw, Ambrose defeated John Cena in a Contract on a Pole match to earn the opportunity to face Rollins in a Hell in a Cell match at the event of the same name. Following weeks of Ambrose attacking Rollins, the duo faced off in a Hell in a Cell match at the Hell in a Cell pay-per-view in October; Rollins won the match when Ambrose was attacked by Bray Wyatt. The next few weeks saw Ambrose and Wyatt taunting and attacking each other in both backstage and in-ring segments, with Wyatt claiming that he could "fix" Ambrose, leading to a match at Survivor Series. Ambrose lost the match by disqualification after utilising weapons, including a table. This led to a TLC match between the two at TLC: Tables, Ladders and Chairs in December. During the match, a television monitor blew up in Ambrose's face, causing Wyatt to ultimately win the match. On Raw the night after, Ambrose stated that his feud with Wyatt was not yet over and at Tribute to the Troops, Ambrose defeated Wyatt in a Boot Camp match. The feud would continue when Wyatt attacked Ambrose during his US Title match with Rusev.