Stockton native Ward, the WBO, WBA, and IBF belt-holder made the shock announcement this afternoon.
The 33-year-old won a gold medal at the 2004 Athens Olympics at light-heavyweight, before embarking on a professional career that saw him win a total of eight world titles across two weight classes.
His last fight was his second consecutive victory over Sergey Kovalev last July.
He'll be remembered as an elusive presence in the ring, a versatile fighter, and a skilled, accurate puncher. He retires with an unblemished record of 32-0-0.
Former middleweight world champion boxer Jake LaMotta has died aged 95.
A native of The Bronx, he was renowned for his aggressive style of fighting and retired with an overall career record of 83-19-4.
He was the subject of 1980 film Raging Bull. Robert De Niro, who portrayed him onscreen, won an Oscar for his performance.
In a statement posted on his Instagram account today British heavyweight David Haye claimed he and Tony Bellew are close to signing a deal to fight once more.
The pair fought in London's 02 Arena last March after an ill-tempered build-up, with the Liverpudlian Bellew stopping Haye in the eleventh round on that occasion.
Haye has subsequently put that defeat down to an achilles injury he suffered early in the fight and questioned whether or not Bellew would be minded towards stepping in the ring with him again.
WBC cruiserweight champion Bellew has had his say on both those issues on social media today.
There was controversy in Las Vegas last night as the Genady Golovkin versus Saul Alverez fight ended in a draw.
With Golovkin out-punching the Mexican and widely seen as the better boxer on the night, one of the judges scored the fight 18-10 in the favour of Canelo whilst another scored the fight as a draw.
The pair will most likely have a rematch, but it's another blow for the sport which has seen plenty 'dodgy' decisions down the years.
Great scenes in Las Vegas this evening with the Gennady Golovkin v Canelo Alvarez weigh-in just moments away, and the crowds are huge in the Arena at the MGM Grand.
There is massive buzz for one of the biggest fights in recent memory, and the Mexican fans are certainly in full voice as they get ready to cheer their man Alvarez on to the scales this evening.
This fight is going to be very special indeed with the winner of this fight set to cement themselves as one of the greatest fighters of their generation, at any weight.