Cena confirmed what fans had been speculating since April, posting to Twitter saying, "For nearly 20 years, the Fast franchise has entertained fans and created some of the biggest cinematic moments in history. It's an incredible honour to join this franchise and this family."
Industry site Deadline first reported the news on Friday (US time), saying the only thing known about Cena's character is that he will be "a bad...".
The official confirmation comes two months after longtime star of the franchise, Vin Diesel, hinted at the addition on his Instagram account.
Diesel said every blue moon, Pablo, his nickname for late co-star and close friend Paul Walker, sends him "another soldier for the fight for truth".
He described the latest cast member as a person who "speaks to what Pablo would have brought me", then panned the camera to reveal John Cena, who was waving and smiling.
Production on Fast 9 is due to start this month, with a release date scheduled for May 22, 2020.