Zach Mitchell joined the Addicks' academy as an U7 and signed his first professional contract with the club in July 2022.

In October 2022, the defender made his first team debut in a Papa John's Trophy tie against Brighton & Hove Albion U21s.

He then made his full league debut for Charlton in December 2022 against Cheltenham Town.

Mitchell was named the Sky Bet League One Apprentice of the Season at the 2023 EFL Awards ceremony following a remarkable breakthrough campaign.

In September 2023, the centre-back joined League Two side Colchester United on a season-long loan.

He signed a new long-term contract with Charlton in October 2024, putting pen-to-paper on a deal until 2027, with a club option of an extra year.