Osborne made his first WWE appearance on the November 7, 2018 episode of 205 Live under the ring name Josh Morrell, where he lost against Lio Rush. Morrell made another appearance on the January 2, 2019 episode of NXT UK, where he lost a match to Wild Boar.
On September 2, 2023, under the name Riley Osborne, he made his official debut with WWE on NXT Level Up in a loss against Javier Bernal. On November 30, Osborne made his debut on Main Event in a losing effort to Apollo Crews.
In December 2023, Osborne was announced as a participant in the NXT Men's Breakout Tournament and was introduced as a student of Chase University. Osborne defeated Keanu Carver in the first round and Lexis King in the semifinals, but lost to Oba Femi in the finals at New Year's Evil on January 2, 2024. Later in January, in an attempt to save Chase U from debt, Osborne and fellow Chase U member Duke Hudson entered the Dusty Rhodes Tag Team Classic but lost in the first round to Joaquin Wilde and Cruz Del Toro of Latino World Order. During this time, Osborne began a romantic relationship with fellow Chase U student Thea Hail and asked her out on a date at NXT Vengeance Day for Valentine's Day, which she accepted. After their date on Valentine's Day didn't end well due to Hail being given advice by Jacy Jayne to play hard to get, Osborne and Hail both agreed to remain friends. On the March 19 episode of NXT, Osborne challenged No Quarter Catch Crew's Drew Gulak for the NXT Heritage Cup but lost 2-1 to Gulak after interference from Jayne and Jazmyn Nyx, who turned against Chase U.
In early May 2024, Ridge Holland started associating himself with Chase U. On the May 14 episode of NXT, Andre Chase offered Osborne to be Holland's tag team partner in his match against The Good Brothers (Luke Gallows and Karl Anderson) to Osborne's dissatisfaction. The Good Brothers won the match after another mishap from Holland. On the May 21 episode of NXT, Fallon Henley defeated Hail to qualify for a spot in the six-woman ladder match to crown the inaugural NXT Women's North American Championship at NXT Battleground. Backstage, Osborne got into an argument with Holland for costing Hail the match, to which Chase proposed that both men settle their differences in the ring where Holland defeated Osborne. After the match, Osborne still do not approve of Chase U working with Holland, with Hudson taking Osborne's side. On the June 4 episode of NXT, Osborne and Hudson refused to walk out with Holland for Hail's match against Jazmyn Nyx. Halfway through the match, Osborne and Hudson showed up to ringside to Hail's surprise, to which Nyx used as an advantage to defeat Hail. On the November 19 episode of NXT, Holland, who had subsequently joined and defected Chase U, defeated Chase with the future of Chase U on the line, causing Chase U to disband.