Liverpool Academy Liverpool signed Sinclair as a 14-year-old from the
West Bromwich Albion youth academy in the summer of 2011. The Liverpool staff compared him to
Raheem Sterling. He spent most of the 2011–12 season with the Under-16s before coach
Mike Marsh gave him a run of four games with the Under-18s at the end of the season. He impressed greatly in those games, though he failed to find the back of the net. On 14 July 2012, Sinclair came off the bench to score a hat-trick against
Exeter City in an Under-18s pre-season friendly. In all, Sinclair netted eight goals in the six Under-18s pre-season friendly games in the run up to the 2012–13 Academy Under-18s season. He went on to score his first competitive goal for the Under-18s on 25 August 2012, hitting a brace in a 3–3 draw with
Crystal Palace.
Reserves and first-team debut 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. He started the match and performed well, winning a
penalty that
Krisztián Adorján converted and going close himself on more than one occasion. 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. For the remainder of the
2012–13 season Sinclair continued to play for Liverpool U18s, but his 2013–14 season was disrupted by injury. Up to the beginning of March 2015, Sinclair scored 22 goals for Liverpool youth teams at various levels, including 6 goals in 7
UEFA Youth League games as well as an impressive finish against
Manchester United U21, beating
Víctor Valdés at his near post, and a solo effort against Chelsea U21. On 16 March 2015, Sinclair was loaned to
Championship side
Wigan Athletic, where he linked up with academy teammate
Sheyi Ojo. 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. 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. On his first appearance of the 2015–16 season, away to
Exeter City in the
FA Cup on 8 January 2016, Sinclair scored his first senior goal for Liverpool in a 2–2 draw. Ten days later he confirmed that he would leave Liverpool at the end of the season, suggesting that he wanted to play in Spain. In April, an offer from
AFC Bournemouth of £4 million plus add-ons was accepted by the club but rejected by the player.
Watford In the January 2016 transfer window, Liverpool had rejected an offer of £1.5 million for Sinclair from Premier League club Watford. On 21 May, Sinclair agreed to join that club when his current contract expired. Because Sinclair was aged under 24, Liverpool were due a developmental fee; the clubs settled on £4 million, and Sinclair signed a five-year contract. He did not make his debut until 3 December, as a 94th-minute substitute in a defeat by West Bromwich Albion, and made his first start a few days later against
Manchester City, a match in which City won at home for the first time since mid-September and
BBC Sport's reporter described Sinclair as "a peripheral figure". 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, and Sinclair scored his first goal for Watford in their FA Cup third-round tie against
Burton Albion on 7 January 2017. Towards the end of the transfer window, Mazzarri stated that Sinclair needed to gain experience and was free to go out on loan if he so wished.
Birmingham City (loan) On 31 January 2017, Sinclair moved to Championship club
Birmingham City on loan until the end of the season. He went straight into the starting eleven for the next match, at home to
Fulham, partnering
Lukas Jutkiewicz, and was replaced after 67 minutes with the score still goalless; Birmingham won the match 1–0. He appeared regularly during February, but the last of his five appearances came as a very late substitute in a home defeat against
Leeds United on 3 March. but the loan was cut short by mutual agreement in January 2019.
Oxford United (loan) On transfer deadline day in January 2019,
Oxford United announced that they had signed Sinclair on loan until the end of the
2018–19 season. His first Oxford goals came in a 2–1 home victory over
Scunthorpe United on 2 March 2019, in which he scored both Oxford goals.
VVV-Venlo (loan) He signed for Dutch club
VVV-Venlo on loan, for the 2019–20 season.
CSKA Sofia (loan) Sinclair moved to
CSKA Sofia on 5 October 2020 on a one-year loan.
As a free agent After a year without a club, Sinclair rejoined Oxford on a trial basis during the 2022–23 pre-season, playing his first match in over a year in a friendly against
Banbury United. 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. ==International career==