[7] Following spells with Fisher Athletic London, AFC Wimbledon and Glebe,[8] Pinnock entered the youth system at Isthmian League club Dulwich Hamlet.

[9] He progressed to be fringe member of the first team squad during the 2010–11 season,[10] which included a spell on loan at Kent County League Premier Division club Holmesdale, during which he was deployed as a utility player.

[13] He made 45 appearances and scored three goals during Rovers' 2016–17 National League playoffs-winning season,[21] which saw the club promoted to the EFL for the first time in its history.

[23] On 30 June 2017, Pinnock signed a three-year contract with Championship club Barnsley for an undisclosed fee,[23] reported to be "in excess of £1 million",[24] plus add-ons.

[31] On 2 July 2019, Pinnock signed a three-year contract with Championship club Brentford, with the option of a further year, for an undisclosed fee,[32] reported to be £3 million.

[33] He displaced Julian Jeanvier and broke into the team alongside Pontus Jansson in November 2019 and his performances after the season restart in June and July 2020 saw him nominated for the PFA Fans' Player of the Month award.

[54][56] After beginning the 2024–25 season as an ever-present starter in league matches,[57] a hamstring injury suffered in December 2024 caused Pinnock to miss six weeks either side of the New Year.

[60] In March 2021, Pinnock was one of six English-born players to receive their first call-up to the Jamaica national team for a friendly match versus the United States.

[66] Pinnock was named in Jamaica's 2024 Copa América squad and started in each group stage match prior to the team's elimination from the tournament.