The Scouser, who had been at the Academy since the age of seven, had scored seven goals in 13 appearances for the U-18 team when he made the bench for the first team at Villa Park in the Carabao Cup on 17 December 2019. Neil Critchley, who managed the Liverpool team against Aston Villa in the absence of Jürgen Klopp who was in Qatar in the Club World Cup, had given Stewart his first taste of the U-23's side when he came on for the second-half in a 1-1 draw with Chelsea four days earlier.

Stewart impressed for both the under 18s and 23s in 2020/21, scoring seventeen times before picking up a knee injury in March. He signed a new long term contract at the end of the season but stayed on the sidelines for much of 2021/22, finally returning to full fitness in April. He remained with the Academy for 2022/23, scoring eleven times in sixteen Premier League 2 appearances and also getting a start for the first team in the League Cup third round tie with Derby County at Anfield. In July 2023 he was sold to Preston for an undisclosed fee, telling his new club's website on completion of the deal: "I’m delighted to be here. It’s another step in my career, on my journey, so I think it’s the right move for my development to try and get some first team football." It was a slow start in his first season however, with all sixteen of his appearances coming as a substitute.