Galloway returned to WWE in April 2017 and joined its then-developmental brand NXT, where he won the NXT Championship at , becoming the first man to win the championship in his TakeOver in-ring debut and the first WWE wrestler to hold it after having previously won a championship on the main roster. Upon returning to WWE's main roster in 2018 he won the Raw Tag Team Championship with Dolph Ziggler, became the winner of the 2020 men's Royal Rumble match, and defeated Brock Lesnar for the WWE Championship in the main event of part 2 of WrestleMania 36. He is the first Scottish-born and British-born world champion in WWE and the thirty-first Triple Crown champion.