In mid-2005 Lashley appeared at four live events, wrestling in dark matches for both the Raw and SmackDown! brands. On September 23, 2005, Lashley made his televised WWE debut as a face on SmackDown!. Lashley was introduced as a three-time National Amateur Wrestling Champion, a four-time All-American, a two-time Armed Forces Champion, and a 2002 Silver Medalist at the Military World Championship. In his first match, he defeated Simon Dean. In his pay-per-view debut at No Mercy, he defeated Dean once again. Lashley went on to defeat numerous superstars both on SmackDown! and Raw. On the November 11 episode of SmackDown!, Lashley defeated Orlando Jordan in a qualifying match for a place on Team SmackDown! at Survivor Series where he was the first to be eliminated. Prior to this elimination Lashley was dominating the Raw Superstars, showcasing various "power moves" and a finisher on Carlito. Yet a chokeslam from Kane, who was on the apron, caused Lashley to be eliminated.
On January 6, 2006, Lashley became the first announced participant from SmackDown! to be entered into that year's Royal Rumble. At the Royal Rumble, Lashley was the eighth wrestler to enter the match. He eliminated Sylvan, but he was then eliminated by the combination of Raw's then World Tag Team Champions The Big Show and Kane. Following the Royal Rumble, Lashley began a feud with John Bradshaw Layfield leading up to a match at No Way Out. The match was Lashley's first loss in singles competition due to interference from Finlay. During February and March, Lashley was involved in a feud with Finlay, where the two would brawl on many occasions, including a lumberjack match that Finlay won after using a shillalegh.
On April 2, after winning a Last Chance battle royal by last eliminating MNM, Lashley competed at his first WrestleMania (WrestleMania 22) in the Money in the Bank ladder match. The match was won by Rob Van Dam. Lashley next entered SmackDown!'s King of the Ring tournament. He lasted until the finals, defeating Mark Henry and Finlay in the process. In the final round, held at Judgment Day he was defeated by Booker T with help from Finlay. Later, as Booker was being crowned, Lashley performed a spear to Booker. These acts developed into a feud with the newly named "King Booker" and the other members of his court (Queen Sharmell, Finlay, and William Regal). During this feud, Lashley won his first professional wrestling championship by defeating JBL for the United States Championship, which he lost to Finlay a little less than two months later. Lashley later joined forces with Batista against the Court. Not long after losing the United States Title, Lashley was declared unable to compete according to a physician who stated that during an annual exam, Lashley was found to have elevated enzymes of the liver and therefore, would not be cleared to wrestle until further evaluation. Lashley returned a couple of weeks later to the SmackDown! roster to continue his feud with the Court and went on to earn his first match for the World Heavyweight Championship at No Mercy against King Booker. This match later became a four way bout that also included Batista and Booker's ally, Finlay. King Booker won that match after pinning Finlay.
On November 14, 2006, Lashley moved to the ECW brand. He debuted on the brand by making a surprise appearance to sign a contract for the final spot in the Extreme Elimination Chamber match for the ECW World Championship at December to Dismember. At December to Dismember, Lashley was the fifth person released into the match. He eliminated both Test and The Big Show by pinfall after a spear to become the new ECW World Champion. This made Lashley the first African American to hold the ECW Title.
After winning the ECW World Championship, Lashley then had successful title defenses against Big Show, Rob Van Dam, Test, Hardcore Holly, Kenny Dykstra, and Mr. Kennedy. On the March 19, 2007, episode of Raw, Lashley officially became the first and only person to ever break Chris Masters' masterlock hold and thus the first and only person to ever defeat the masterlock challenge.
In early 2007, Lashley was selected by Donald Trump to represent him in a "Battle of the Billionaires" match, against Vince McMahon's representative, Umaga which also featured Vince's long time adversary Stone Cold Steve Austin as the guest referee. At WrestleMania 23 in a Hair vs. Hair match, Lashley defeated Umaga following a spear and helped Trump shave McMahon's head afterwards in accordance with the match's losing stipulation. After WrestleMania, Lashley feuded with Mr. McMahon. McMahon booked himself, his son Shane McMahon, and Umaga in a 3 on 1 handicap match against Lashley at Backlash for the ECW World Championship. After two high impact diving splashes from Umaga, Mr. McMahon tagged himself into the match and pinned Lashley to win the title. Lashley injured his shoulder during the match and after an examination days later, it was revealed he had a damaged rotator cuff but would not need surgery at the time. At Judgment Day, Lashley defeated Vince, Shane, and Umaga in a 3 on 1 handicap rematch after hitting the Dominator on Shane McMahon. Lashley did not win the ECW World Championship, however, because he did not pin Mr. McMahon. As a result, Mr. McMahon retained the title. On June 3 at One Night Stand, Lashley defeated Vince McMahon in a street fight to win the ECW World Championship for a second reign despite interference by Shane McMahon and Umaga in the match, making Lashley the first man to win the ECW World Championship twice since WWE reactivated the title.
On the June 11 edition of Raw, Lashley was drafted from the ECW brand to the Raw brand as part of the 2007 WWE Draft, as a result of the drafting, Lashley had the ECW World Championship taken from him. He took place in a challenge match against Mick Foley, Randy Orton, King Booker and John Cena for the WWE Championship at Vengeance: Night of Champions which Cena won to retain the WWE championship. Lashley became the number one contender for the WWE Championship by winning the "Beat the Clock" challenge on the July 2 edition of Raw. On July 22 at The Great American Bash, he was pinned and defeated by John Cena, after the match they shook hands as a sign of respect, this was Lashley's final WWE pay-per-view appearance. On July 30 episode of Raw, Lashley was defeated by Mr. Kennedy. During the match Lashley was "injured" after Kennedy kicked Lashley's shoulder into the ring steps, allowing Lashley to have time off for surgery for the legitimate injury he suffered at Backlash, this was Lashley's final appearance in WWE.
WWE announced that Lashley was released from his WWE contract on February 4, 2008.