In February 2021, WWE announced that they had signed Breakker to a contract. Later that month, he was assigned to the WWE Performance Center in Orlando, Florida for training. At the WrestleMania Backlash pay-per-view on May 16, 2021, Breakker and several other wrestlers portrayed "zombies" in a lumberjack match between Damian Priest and The Miz. On the September 14 episode of NXT, he made his debut defeating LA Knight. He then had a staredown with NXT Champion Tommaso Ciampa to end the show. Breakker was subsequently scheduled to challenge Ciampa for the title at the Halloween Havoc television special on October 26, where he would go on to lose. On December 5 at NXT WarGames, Breakker teamed with Carmelo Hayes, Grayson Waller, and Tony D'Angelo (as "Team 2.0") to defeat Ciampa, Knight, Johnny Gargano, and Pete Dunne ("Team Black and Gold") in a WarGames match, with Breakker pinning Ciampa. At New Year's Evil on January 4, 2022, Breakker defeated Tommaso Ciampa with the Steiner Recliner for the NXT Championship. At NXT Vengeance Day on February 15, Breakker retained the title against Santos Escobar. Breakker made his main roster debut on the March 7, 2022 episode of Raw, teaming with Ciampa to defeat Dolph Ziggler and Robert Roode in a tag team match. The next night at NXT Roadblock, Breakker lost the NXT Championship to Ziggler in a triple threat match also involving Ciampa, ending his reign at 63 days. On April 1, Breakker inducted his father and uncle into the WWE Hall of Fame; the following night at Stand and Deliver, he challenged Ziggler for a rematch for the title, but ultimately failed to regain the belt. On the April 4 episode of Raw, Breakker defeated Ziggler to begin his second reign as NXT Champion. Breakker subsequently began feuding with Joe Gacy after Gacy kidnapped Rick Steiner. On May 3 at Spring Breakin', he defeated Gacy to retain his title. At NXT In Your House the next month, Breakker defeated Gacy once more to retain the title. At the Great American Bash on July 5, Breakker retained the title against Cameron Grimes, and was attacked by the debuting JD McDonagh after the match. At Heatwave on August 16, Breakker retained the title against McDonagh; after the match, he was confronted by NXT United Kingdom Champion Tyler Bate. At Worlds Collide on September 4, Breakker defeated Bate to unify the NXT and NXT UK Championships, becoming the first and only non-European wrestler to win the title. At Halloween Havoc in October, Breakker defeated Ilja Dragunov and JD McDonagh in a triple threat match to retain the NXT Championship. On December 10, Breakker defended his championship in a winning effort against Apollo Crews at NXT Deadline.
At New Year's Evil on January 10, 2023, Breakker defeated Grayson Waller via countout to retain the NXT Championship. At Vengeance Day on February 4, he defeated Waller once again, this time in a cage match. At Stand & Deliver on April 1, Breakker lost the NXT Championship to Carmelo Hayes, ending his reign at 362 days. On the April 4 episode of NXT, Breakker attacked Hayes, turning heel. He cemented his new villainous persona the next week, after interrupting Chase University in the ring, verbally insulting the audience, and attacking Andre Chase. At Spring Breakin' on April 25, Breakker defeated Chase via submission. At Battleground on May 28, Breakker failed to regain the NXT Championship from Hayes. At NXT Gold Rush on June 20, he unsuccessfully challenged Seth Rollins for the World Heavyweight Championship. At Heatwave on August 22, Breakker attacked Von Wagner, and on the September 6 episode of NXT, he bludgeoned Wagner with a set of steel steps. Later that month, Breakker took part in the Superstar Spectacle live event in India, where he defeated Odyssey Jones. At NXT No Mercy on September 30, Breakker lost to Baron Corbin. On the October 10 episode of NXT, Breakker (with Paul Heyman in his corner) lost to Carmelo Hayes (with John Cena in his corner; following the match, Breakker attacked Hayes, prompting The Undertaker to come to the ring and chokeslam Breakker. At Halloween Havoc later that month, Breakker defeated Mr. Stone. On the November 28 episode of NXT, Breakker defeated Eddy Thorpe to qualify for the Iron Survivor Challenge at NXT Deadline, which was won by Trick Williams.
Breakker later entered the Dusty Rhodes Tag Team Classic tournament in January 2024, pairing with Baron Corbin to defeat Gallus (Mark Coffey and Wolfgang) in the first round and Axiom and Nathan Frazer in the semifinals. Breakker made his Royal Rumble match debut at the titular event as the number twenty entrant, eliminating Finn Bálor, Ivar, Jimmy Uso, and Omos before being eliminated by "Dirty" Dominik Mysterio. At NXT Vengeance Day the following month, Breakker and Corbin defeated Carmelo Hayes and Trick Williams to win the Dusty Rhodes Tag Team Classic. The following night on Raw, Breakker made his second appearance on the main roster in a backstage segment with Imperium, debating whether he should sign to Raw or SmackDown. On the February 13 episode of NXT, the Wolf Dogs defeated The Family (Tony D'Angelo and Channing "Stacks" Lorenzo) to win the NXT Tag Team Championships.
On the February 16 episode of SmackDown, SmackDown General Manager Nick Aldis announced that Breakker had officially joined SmackDown, bringing him on stage to sign his contract and confirming his call-up to the main roster in the process. The following week, Breakker made his in-ring debut for the brand, defeating Dante Chen.
At NXT Roadblock in March 2024, the Wolf Dogs successfully defended the titles against Chase U. On April 6 at Stand and Deliver, the Wolf Dogs defeated Axiom and Nathan Frazer to retain the titles. In a rematch on the April 9 episode of NXT, Frazer and Axiom defeated the Wolf Dogs, ending their reign at 57 days. During the WWE Draft in April, Breakker was drafted to the Raw brand. On the May 20 episode of Raw, Breakker turned heel after his match with Kale Dixon, when he continued to attack Dixon after the match. On the June 17 episode of Raw, Breakker interrupted WWE Intercontinental Champion Sami Zayn, stating that he wanted Zayn's championship. This led to a match between Breakker and Zayn being scheduled for Money in the Bank. At the event on July 6, Breakker was unsuccessful in winning the title. During a rematch on August 4 at SummerSlam, Breakker successfully pinned Zayn, beginning his first reign as Intercontinental Champion. On the August 12 episode of Raw, Breakker defeated Zayn to retain the title in a two-out-of-three falls match, ending their feud. On the September 23 episode of Raw, Breakker lost the title to Jey Uso, ending his reign at 51 days. On the October 21 episode of Raw, Breakker defeated Uso to regain the Intercontinental Championship after interference by The Bloodline. At Survivor Series WarGames on November 30, Breakker successfully defended the title against Ludwig Kaiser and Sheamus in a triple threat match.