The 33-year-old Reigns, whose real name is Joe Anoa'i, made the announcement Monday night to open the episode of "Raw."
He was originally diagnosed in 2008 at age 22, though he quickly went into remission. He's been fighting the disease since.
Anoa'i, who played football at Georgia Tech, has appeared in the last four main events at WrestleMania. The WWE's universal champion said during the announcement that he plans on returning to the ring when he gets healthy.
"Reigns is taking his battle with leukemia public in an effort to raise awareness and funds for research in order to advance cures for the disease," WWE said in a statement.
MESSAGES FROM FANS AND FELLOW WRESTLERS FOR ROMAN REIGNS
.@WWERomanReigns YOU gave us the gift of your work ethic in NXT. You gave us the gift of your athleticism & determination in the ring. You gave us the gift of your knowledge in the locker room. But your comeback match will be the greatest gift of all. We are all looking fwd to it— Charlotte Flair (@MsCharlotteWWE) October 23, 2018
Friend @WWERomanReigns , you have my prayers and your family is your greatest support!! This will pass and you will come back stronger than before. Your health is what matters!! Take care of you! pic.twitter.com/2ql3aasJyq— Mohamed Azharudeen.M (@azharBDM) October 23, 2018