On December 15, 2016, McDonagh (as Jordan Devlin) was announced as one of sixteen men competing in the first ever United Kingdom Championship Tournament to crown the first ever WWE United Kingdom Champion on January 14 and 15, 2017. Devlin defeated Danny Burch in the first round, advancing to the quarter finals, where he was defeated by Tyler Bate. Devlin also appeared at several WWE live shows. On May 18, 2018, WWE announced that Devlin would be one of sixteen contestants in the second annual United Kingdom Championship Tournament. He would defeat Tyson T-Bone in the first round, but lost to Flash Morgan Webster in round two.
After some disagreements in the beginning episodes of NXT UK, a fight against Travis Banks was agreed in NXT UK TakeOver: Blackpool. However, that night both competitors attacked each other before the bell was hit, with Banks being the most affected. Devlin, getting into the ring, referred to himself as Ireland's best fighter. He was interrupted by the general manager of the brand, Johnny Saint, who went out to agree to a fight against an unknown fighter who turned out to be Finn Bálor, who won with a coup de grace.
On January 26 and 27, Devlin participated in the Worlds Collide tournament which featured superstars from NXT, 205 Live, and NXT UK. He won a fifteen-man battle royal to earn a bye in the first round. He defeated Drew Gulak in the quarterfinals while being eliminated by Velveteen Dream in the semifinals.
At Worlds Collide 2020, Devlin won a fatal four-way match, defeating Travis Banks, Isaiah "Swerve" Scott, and Angel Garza to become the new NXT Cruiserweight Champion. Devlin would go on to successfully defend the title all over NXT, NXT UK and 205 Live against opponents such as Lio Rush, Tony Nese, Tyler Breeze and Travis Banks. In April 2020, it was revealed that Devlin was unable to defend the Cruiserweight Championship. This led to the announcement of a tournament to crown an interim Cruiserweight Champion, which was won by Santos Escobar. Devlin responded by calling whoever won the tournament a "fraud" and stating that he would prove himself as the true Cruiserweight Champion upon his eventual return. On March 10, 2021, it was revealed that Devlin would appear in NXT on the following week to enter into his feud with the interim Cruiserweight Champion Santos Escobar. On night two of NXT TakeOver: Stand and Deliver, Escobar defeated Devlin to end his reign at 438 days.
The following week, Devlin confronted Ilja Dragunov in the ring. Although he did not say anything, he made his intentions to challenge Dragunov for the NXT UK Championship clear. Devlin faced Ilja Dragunov in an empty arena, but failed to capture the NXT UK Championship. After trading verbal shots with Ilja Dragunov, Devlin would get another chance at the NXT UK Championship, under the stipulation that the loser would leave NXT UK. The match would take place on the two-hundredth episode of NXT UK, where Devlin failed to win the title. This marked his final appearance for the brand.
On the June 21 episode of NXT 2.0, a vignette aired announcing Devlin's official arrival on the NXT brand, now under the ring name JD McDonagh. McDonagh would make his re-debut as a heel by attacking NXT Champion Bron Breakker after his match with Cameron Grimes on July 5, at NXT The Great American Bash. On the July 12 episode of NXT 2.0, McDonagh would interrupt Cameron Grimes on stage and attack him, only for the latter to retaliate, thus setting up a match for the following week; McDonagh would be victorious in their bout the next week. At NXT Heatwave on August 16, McDonagh unsuccessfully challenged Breakker for the NXT Championship. McDonagh received another title shot at Halloween Havoc on October 22, in a triple threat match also involving Ilja Dragunov, but once again failed to win the title.
As part of the 2023 WWE Draft, McDonagh was drafted to the Raw brand. In his debut match on the May 29 edition of Raw, he fought Dolph Ziggler to a double count-out draw. Following this, McDonagh started appearing in backstage segments with his real-life mentor Finn Bálor, a member of the Judgment Day stable. After being pulled from television for a few weeks, McDonagh returned on the August 7 episode of Raw, seemingly sewing seeds of dissension between Bálor and the other members of the Judgment Day. At Payback, McDonagh interfered alongside The Judgment Day in Bálor and Damian Priest's street fight victory against Kevin Owens and Sami Zayn for the Undisputed WWE Tag Team Championships. On the following episode of Raw, McDonagh gave Priest a customized Money in the Bank briefcase. Later that night, McDonagh defeated Zayn to win his first match on the main roster after interference from Dominik Mysterio. In the following weeks, McDonagh would aid the group in their matches, including helping Mysterio recapture the NXT North American Championship on the October 3 episode of NXT. On the November 13 episode of Raw, McDonagh officially joined The Judgment Day after Priest gave him a new jacket. McDonagh participated in his first WarGames match at Survivor Series: WarGames alongside The Judgment Day and Drew McIntyre against Cody Rhodes, Sami Zayn, Jey Uso, Seth Rollins and a returning Randy Orton on November 25, in a losing effort. During the closing stages of the match, McDonagh was thrown off the cage by Zayn and Rollins into an RKO from Orton. On the December 18 episode of Raw, McDonagh was defeated by R-Truth in a Miracle on 34th Street Fight with a "Loser Leaves the Judgment Day" stipulation. Later that night, Priest informed McDonagh that he was still a part of The Judgment Day, despite losing the match. At the Royal Rumble on January 27, McDonagh entered the match at number twenty-three and lasted only three seconds before being eliminated by Jey Uso after a distraction from R-Truth. On the June 24 episode of Raw, with the help of Liv Morgan, McDonagh and Bálor defeated World Tag Team Champions The Awesome Truth (The Miz and R-Truth) for the titles.