Bettinelli started his career at Fulham at the age of 14 and made his club debut at the start of the 2014/15 season, following their relegation to the Championship. After establishing himself as first-choice goalkeeper at Fulham in 2014, he earned international recognition with a call-up to the England Under-21s squad. Marcus Bettinelli joined Chelsea in July 2021 after spending time on loan to Dartford, Accrington Stanley and Middlesbrough.