Maddison began his career with Coventry City before joining Norwich City in 2016. He spent the 2016–17 season on loan at Scottish Premiership club Aberdeen. In his first season back at Norwich, Maddison was named in the Championship PFA Team of the Year and EFL Team of the Season. He joined Premier League club Leicester City in 2018.
Maddison made his England under-21 debut in the 2019 UEFA European Under-21 Championship qualification and was called up to the senior team in 2019.