Demetri Mitchell joined Exeter City for an undisclosed fee from Hibernian in January 2023. He was one of six City signings in the January transfer window and, after making an immediate impression, missed an entire year through injury.

Demetri was a member of Manchester United academy teams from the age of ten becoming a scholar in 2013 and later signing professional. He made his first-team debut, as a starter, against Crystal Palace in the final league game of the season in May 2017. That was to be his only first-team appearance, and after two loan spells at Hearts, Demetri left Old Trafford for Blackpool in 2020. Whilst at Manchester United he had played for England at under-16 level through to under-20 and was part of the squad which won the 2014 European Under 17 Football Championship.

At Blackpool Demetri saw promotion to the Championship before signing for Hibernian for an undisclosed fee in January 2022. He was to spend almost exactly a year at Easter Road, making nine league appearances, before joining Exeter early in 2023.

Demetri made his Exeter debut on 28 January 2023 as a substitute at MK Dons and scored his first City goal against Charlton Athletic on 4 February 2023 with another against Accrington soon following. Moving into his first full season with the Grecians, he scored the winner when City beat Premier League Luton Town in the League Cup in September 2023 but then, after showing fine form over a number of games (with goals against Carlisle and Leyton Orient), he suffered a serious knee injury against Middlesbrough in the next round of the League Cup and did not feature again that season. 

Still not fully-recovered by the summer of 2024, Demetri nonetheless signed a contract extension for the duration of the 2024/25 season and eventually returned to the first-team squad - after an absence of 364 days - for the EFL Trophy tie at Bristol Rovers on 29 October 2024 when he scored a late goal after coming off the bench.