England international Grealish has spent his entire career at Aston Villa and has been captain of the club since 2019.
The 25-year-old played a pivotal role in helping Villa retain their top-flight status at the end of the 2019-20 season, after which he was heavily linked with a move to Manchester United.
He instead signed a new long-term contract but, after scoring six league goals and adding a further 10 assists across 26 appearances in the 2020-21 campaign, Grealish has now made the move north to Manchester.