On February 11, 2019, Grimes began working at the WWE Performance Center. Shortly after he started appearing at NXT live events in the Florida area, he made his Full Sail University debut in a dark match before the May 1 NXT television tapings, defeating Shane Strickland. That same month, it was announced that Grimes would compete in a tournament named the NXT Breakout Tournament, where he made his debut on the July 3 episode of NXT, defeating Isaiah "Swerve" Scott in the first round of the tournament. On the July 31 episode of NXT, Grimes defeated Bronson Reed to move on to the final round against Jordan Myles. In the finals, he was defeated by Myles. On September 18, Grimes defeated Sean Maluta on NXT's debut on the USA Network. Over the next few weeks, Grimes would develop a winning streak defeating the likes of Raul Mendoza and Boa. On the October 23 episode of NXT, Grimes was defeated by Matt Riddle. Grimes would begin a feud with Kushida when he attacked him backstage after Kushida had beat him. On the December 11 edition of NXT, Kushida cost Grimes his match against Raul Mendoza and would taunt him by stealing his signature hat. The following week, Grimes defeated Kushida to end the feud. After defeating Dominik Dijakovic on the Feb 26, 2020 episode of NXT, Grimes would issue a challenge to Keith Lee for the NXT North American Championship which Lee accepted. On March 11, 2020, he faced Keith Lee for the North American Championship in a losing effort. On the May 6 episode of NXT, he defeated Denzel Dejournette, but was attacked by Finn Balor after the match, who Grimes had called out earlier. The following week, Grimes defeated Balor in a match following a distraction by Damian Priest. Grimes would go on to flaunt his victory over Balor while mocking Priest for losing to Balor at NXT TakeOver: In Your House and calling him a loser, which led to Priest attacking him backstage. On the June 17 episode of NXT, Priest found the tires of his Dodge Challenger to be punctured which turned out to be done by Grimes who once again mocked Priest. Priest would challenge Grimes to a match the following week. Prior to the match, Priest was attacked and came into the match injured, giving Grimes the victory. A rematch was scheduled on the June 24 episode of NXT in which Grimes lost. On the August 12 episode of NXT, Grimes defeated Velveteen Dream and Kushida to qualify for the NXT North American Championship ladder match at NXT TakeOver: XXX. At the event, Grimes was unsuccessful at capturing the title.
On the September 23 episode of NXT, Grimes competed in the first ever Gauntlet Eliminator match to determine the number one contender for the NXT Championship at NXT TakeOver: 31 against Finn Balor, losing to Kyle O'Reilly. Grimes then entered a feud with Dexter Lumis, attacking him on the October 7 episode of NXT after his match with Austin Theory. After distracting him during his North American Title match against Damian Priest the following week, Grimes was put in a Haunted House of Terror match against Lumis on October 28 at NXT Halloween Havoc, losing to him in the ring by submission. On the November 11 episode of NXT, Grimes interfered in Lumis's match against Timothy Thatcher, subsequently wrapping his head in a burlap sack and attacking him. The following week, they faced off in a blindfold match which ended in an apparent no contest after Grimes unknowingly knocked the referee unconscious and eventually ran off. He would lose to Lumis again in a strap match on December 6 at NXT TakeOver: WarGames. On the December 9 episode of NXT, Grimes would be defeated by Tommaso Ciampa, then attacked by Timothy Thatcher after the match because Grimes had angrily questioned Thatcher about being at ringside. It was announced the following week that Grimes was out injured for four to six weeks after Thatcher's attack. Grimes returned on the February 10, 2021 episode of NXT with a new gimmick as he claimed to have become a millionaire during his time away, thus making him the "richest man in NXT". He then failed to win a gauntlet match at NXT TakeOver: Stand and Deliver for a future North American Championship match. On the April 27 episode of NXT, Grimes began a feud with WWE Hall of Famer Ted DiBiase after encountering him in a jewelry store over their watches. Over the next few weeks, "The Million Dollar Man" would continue to one-up Grimes, outbidding him in various purchases, and would end up costing Grimes a match to Jake Atlas on May 18. The two then had a "Million Dollar Face-Off" on the May 25 episode, where LA Knight attacked Grimes and aligned himself with DiBiase, turning Grimes face for the first time in his WWE career. On the June 8 episode, DiBiase reintroduced the Million Dollar Championship and announced that the winner of a ladder match between Grimes and Knight at NXT TakeOver: In Your House would win the title, where Grimes was unsuccessful. On the following episode of NXT, Grimes would save DiBiase from an attack by Knight, confirming his face turn. Grimes would subsequently challenge Knight to a rematch for the title at The Great American Bash, under the stipulation that if he lost, he would be forced to become Knight's butler. At the event, Grimes failed to win the title and as a result, was forced to become Knight's butler. At NXT TakeOver: 36, Cameron Grimes faced LA Knight for the Million Dollar Championship once again, where if he lost, Ted DiBiase would become LA Knight's butler. Grimes defeated Knight at the event and won his first Million Dollar Championship.
Grimes faced Carmelo Hayes for the NXT North American Championship at the Vengeance Day special episode of NXT 2.0 on February 15, 2022, which he lost. On April 2, at NXT Stand and Deliver, Grimes would win the NXT North American Championship by defeating Carmelo Hayes, Santos Escobar, Solo Sikoa and Grayson Waller in a fatal five-way ladder match. He made his first successful title defense against Solo Sikoa on the April 12 episode of NXT 2.0. Grimes would make another successful title defense in a triple threat match at NXT Spring Breakin' against Carmelo Hayes and Solo Sikoa. At NXT In Your House, Grimes lost the North American Championship to Hayes, ending his reign at 65 days. Grimes then entered a rivalry with NXT Champion Bron Breakker, whom he lost to at NXT The Great American Bash. On the July 12 edition of NXT 2.0, Grimes would cut an emotional promo, only for JD McDonagh to interrupt and attack him. However, Grimes would retaliate, thus setting up a match for the following week, which McDonagh would win. Shortly after, he entered a feud with Joe Gacy as the latter claimed that he could be his father figure as Grimes lost his real life father years prior. During this rivalry, the debuting Ava Raine would join Gacy's stable Schism and cost Grimes in his final match with Gacy on the November 8 episode of NXT.
As part of the 2023 WWE Draft, Grimes was drafted to the SmackDown brand. Grimes would make his main roster debut on the May 12 episode of SmackDown, defeating Baron Corbin in six seconds. After that, Grimes mainly appeared in enhancement roles, quickly losing matches to stars like Bron Breakker. On April 23, 2024, Grimes announced that he had been released from WWE.