Jerome spent his youth at West Bromwich Albion and Liverpool, making his senior debut for the latter at the age of 16 years and 6 days in 2012, their youngest player of all time.

[5] He began playing organised football as a seven-year-old with Phoenix United, part of a scheme designed to use sport to keep youngsters off the streets and promote positive values.

He was spotted while playing for Phoenix United, invited to a trial with West Bromwich Albion, and joined that club as a schoolboy at the age of eight.

[citation needed] While still only 15, Sinclair was called up to Rodolfo Borrell's NextGen Series side for the away match with defending champions Inter Milan in September 2012, after first-team manager Brendan Rodgers included a number of young players in his Europa League squad.

[15] Rodgers called Sinclair up to the first team for the League Cup third-round tie away to his boyhood club, West Bromwich Albion, on 26 September.

At the age of 16 years and 6 days, he came off the bench in the 81st minute to replace Samed Yeşil in the 2–1 win at The Hawthorns, thus breaking Jack Robinson's record as Liverpool's youngest ever player.

[17] He was one of several youngsters to travel to a Europa League tie against Beşiktaş in February, but was not included in the matchday squad as Liverpool were eliminated on penalties.

[21] The next day, he made his Football League debut in what proved to be his only Wigan appearance, replacing Marc-Antoine Fortuné for the final eight minutes of a 2–0 loss to Watford at the DW Stadium.

[22] On returning to Liverpool, Sinclair made his Premier League debut as a 68th-minute substitute for Rickie Lambert in a 1–1 draw away to champions Chelsea on 10 May.

[30] An approach in late December by Championship club Brentford to take him on loan was rebuffed because manager Walter Mazzarri felt he was needed as cover,[31] and Sinclair scored his first goal for Watford in their FA Cup third-round tie against Burton Albion on 7 January 2017.

[44] However, he did not earn a contract, and by January 2023, he appeared to have stepped away from football to focus on other business interests, including owning a branch of fried chicken chain Morley's.