Fish made his debut in WWE's developmental territory NXT at the June 23, 2017 television tapings, losing to Aleister Black. Triple H confirmed Fish's signing on July 12.
At NXT TakeOver: Brooklyn III, Fish, alongside Kyle O'Reilly (who had also signed with WWE), attacked SAnitY after they defeated The Authors of Pain to win the NXT Tag Team Championships. Later on in the night, the two assisted the debuting Adam Cole in attacking newly crowned NXT Champion Drew McIntyre, turning Fish heel in the process. The following month, the trio of Fish, Cole and O'Reilly was officially dubbed "The Undisputed Era". On the September 27 episode of NXT, O'Reilly and Fish were at ringside when Cole defeated Eric Young. On the October 4 episode of NXT, after Roderick Strong's match with McIntyre, The Undisputed Era walked out and patted Strong on the back, signaling an alliance. On the October 11 episode of NXT, The Undisputed Era appeared at the top of the entrance ramp alongside former Mae Young Classic competitor Taynara Conti. At the encouragement of The Undisputed Era, Conti distracted SAnitY member Nikki Cross and prevented her from scoring a pin, ensuring Cross wouldn’t advance to the NXT Women's Championship Fatal 4-Way Match at NXT TakeOver: WarGames. On the October 18 episode of NXT, The Undisputed Era faced SAnitY to a no contest. On the October 25 episode of NXT, The Undisputed Era gave Strong an Undisputed Era armband, with Cole telling Strong that he is “not a loser” and offering him a position in their group. On the November 1 episode of NXT, The Undisputed Era attacked both SAnitY and The Authors of Pain during their NXT Tag Team Championship match. During a three-team brawl, Strong emerged and appeared to assist The Undisputed Era, only to attack them. During the fight, NXT general manager William Regal announced that The Undisputed Era would be involved in a WarGames match at NXT TakeOver: WarGames against SAnitY and the team of Strong and The Authors of Pain. At the event, The Undisputed Era emerged victorious in the first War Games match in over 17 years. On the December 20 episode of NXT, Fish and O'Reilly defeated SAnitY to win the NXT Tag Team Championship. On the January 10 episode of NXT, The Undisputed Era attacked SAnitY before their NXT Tag Team Championship rematch. In their place, Strong and Aleister Black challenged for the titles, but were defeated. At NXT TakeOver: Philadelphia, Fish and O'Reilly defeated The Authors of Pain to retain the NXT Tag Team Championships. Later in the night, the two assisted Cole in his Extreme Rules match against Black, but SAnitY evened the odds which allowed Black to be victorious. On March 4, Fish suffered a torn ACL and torn MCL in his left knee at an NXT live event. He later underwent surgery and would be out of action for six months. On October 17, Fish returned to NXT to attack The War Raiders, thus helping his fellow Undisputed Era members Kyle O'Reilly and Roderick Strong to keep their belts.
On June 1, 2019 at NXT TakeOver: XXV, Fish and O'Reilly faced The Street Profits (Angelo Dawkins and Montez Ford), The Forgotten Sons (Wesley Blake and Steve Cutler), and Oney Lorcan and Danny Burch in a fatal-4 way ladder match for the vacant NXT Tag Team Championships, but the match was won by Dawkins and Ford. Fish and O'Reilly later challenged The Street Profits for the titles at NXT TakeOver: Toronto on August 10, but again failed to become the champions. Six days later on the August 16 tapings of NXT, however, O'Reilly and Fish finally defeated The Street Profits for the NXT Tag Team Championship. They successfully defended the titles in a rematch against The Street Profits on the October 2 episode of NXT. At NXT TakeOver: WarGames, The Undisputed Era were defeated by Team Ciampa in a WarGames match. The next night, at Survivor Series, Fish and O'Reilly would face The New Day and The Viking Raiders in a triple threat tag team match, but would be defeated as The Viking Raiders won the match. Heading into 2020, Fish and O'Reilly would enter the Dusty Rhodes Tag Team Classic and would defeat Gallus in the first round, but would be defeated by The Grizzled Young Veterans in the second round. The Undisputed Era would enter a brief feud with Imperium and it would be announced that the two factions would face each other at Worlds Collide. At the event, Imperium defeated The Undisputed Era. At NXT TakeOver: Portland, Fish and O'Reilly dropped the titles to The BroserWeights (Pete Dunne and Matt Riddle), ending their reign at 172 days. Over the summer, The Undisputed Era would slowly turn face as they assisted Cole in his feud with Pat McAfee, which culminated in a WarGames match at NXT TakeOver: WarGames, where The Undisputed Era defeated Team McAfee. However during the match, Fish would suffer an injury to his triceps, taking him out of action once again. During his absence, The Undisputed Era disbanded following Cole's betrayal over O'Reilly and Strong.
Fish returned on the May 11, 2021 episode of NXT, as a face, saving O'Reilly from an attack by Pete Dunne and Oney Lorcan. Fish would then make his in-ring return on the May 25 episode, where he faced Dunne in a losing effort. On the August 3 episode of NXT, Fish was defeated by former Undisputed Era teammate, Roderick Strong. On August 6, Fish was released from his WWE contract.