Willis started playing rugby as a child at Reading Abbey, following in the footsteps of his father Steven and older brother Jack.
[9] Throughout the 2022–23 Top 14 season, Willis made 17 appearances, which included 13 starts, and scored two tries, to support the team's run to the play-off semi-final, where they were defeated by La Rochelle.
[13] Willis established himself as the first-choice Number 8 at Saracens for the 2024–25 Premiership season, following the departure of long-serving club stalwart Billy Vunipola.
[16] He was included in the squad for the 2018 World Rugby Under 20 Championship and came off the bench in the final as England finished runners up to hosts France.
[19] In 2023, England head coach Steve Borthwick included Willis in the training squad for the 2023 Rugby World Cup.