Mills joined
Everton from
Leeds United in 2018. In July 2021, he signed his first professional contract, signing a two-year deal. In July 2022, he made the first team squad for a pre-season tour of the USA. The following month, after making his first team debut on tour, he extended his contract until 2025. On 23 August 2022, he made his professional debut as a substitute in a 1–0 win over
Fleetwood Town in the
EFL Cup. On 27 July 2023, Mills joined
League One club
Oxford United on a season-long loan deal. The loan deal was cut short in January 2024 after he suffered a serious knee injury and returned to Everton for treatment.
Oxford United On 31 January 2025, Mills returned to Oxford on a permanent deal. Although the season ended in disappointment as Oxford United were relegated from the
Championship, Mills was named Player of the Season for the
2025–26 season. ==Personal life==