Ward announced his decision Thursday, saying his "body can no longer put up with the rigors of the sport."
Unified light heavyweight world champion Andre Ward said via a statement on his website that he is "leaving" boxing.
He tweeted out the link along with the words "Mission Accomplished" and the peace-out emoji.
"I want to be clear—I am leaving because my body can no longer put up with the rigors of the sport and therefore my desire to fight is no longer there," he said. "If I cannot give my family, my team, and the fans everything that I have, then I should no longer be fighting."
Ward, 33, was 32-0 (16 KOs), and he last won an eighth-round match June 17 against Sergey Kovalev to defend his light heavyweight boxing title in a rematch from the two's November 2016 bout.
Last month, Ward told media that his television contract with HBO was up, but he was still under contract with promoter Roc Nation Sports.
Before turning pro in 2004, Ward won an Olympic gold medal at Athens in 2004, becoming the only male American boxer to win do this in the last decade.