On May 16, 2018, it was revealed that Coffey would be one of sixteen men competing in a one-night tournament to face Pete Dunne for the WWE United Kingdom Championship. He would defeat Tucker and Dave Mastiff in the first and second round, respectively, before losing to Travis Banks in the semi-finals.
Coffey would then go on to be a mainstay of NXT UK, being accompanied by his brother Mark Coffey in a winning effort in the first ever televised match on NXT UK and later forming the stable Gallus with his brother and Wolfgang to feud with British Strong Style. Coffey main evented the inaugural NXT UK TakeOver in Blackpool on January 12, 2019, as he challenged Pete Dunne for the WWE United Kingdom Championship but failed to capture the title. After the match, he was attacked by the debuting Walter. At NXT UK TakeOver: Cardiff, Coffey defeated Dave Mastiff in a Last Man Standing match.
On August 23, 2022, Coffey along with Gallus (Mark Coffey and Wolfgang) would debut on NXT, facing NXT UK Tag Team Champions Brooks Jensen and Josh Briggs, where they would go on to win via countout.
On the May 14, 2024 episode of NXT, Gallus were revealed as the attackers of Wes Lee, Josh Briggs and Ivar backstage, making their first televised appearance on NXT since the February 13, 2024 episode. Later, NXT General Manager Ava announced that Joe would replace Ivar in a triple threat match to determine the number one contender to the NXT North American Championship. The following week, both Coffey and Lee pinned Briggs, and the two men were considered the winner. Later that night, Ava set up a triple threat match between Coffey, Lee and Oba Femi for the NXT North American Championship at NXT Battleground, which Femi would ultimately win.