"He has passed - he's gone home," Steward's sister Diane Steward-Jones told the Detroit Free Press by phone. "He was in no pain, and we sang to him, as well as did the doctors present. He had loved ones around him."
Steward's girlfriend Anita Ruiz, who is also executive director of the Kronk Gym Foundation, told Reuters the trainer had died after having "complications through surgery" for diverticulitis.
Steward ended his amateur career with a record of 94 wins and three losses but is best known as the trainer who transformed Thomas Hearns from a light-hitting boxer into a devastating puncher.
Under Steward's guidance, 'Hitman' Hearns became a four-division welterweight champion in the 1980s as he vied with fellow boxing greats such as Sugar Ray Leonard, Roberto Duran and Marvin Hagler.
Most recently, Steward trained heavyweight world champion Wladimir Klitschko before he was forced to step aside because of an undisclosed illness.
"It is not often that a person in any line of work gets a chance to work with a legend, well I was privileged enough to work with one for almost a decade," Ukrainian Klitschko said in a statement.
"I will miss our time together. The long talks about boxing, the world, and life itself. Most of all I will miss our friendship.
"My team and I will carry on with the goals we had set while Emanuel was with us because that is exactly what Emanuel would have wanted ... we will accomplish these goals in his honour."
West Virginia native Steward was central to the famous Kronk Gym in Detroit where he helped shape the careers of fighters such as Hilmer Kenty and Milton McCrory. Later he worked with British and Canadian world heavyweight champion Lennox Lewis.
"This has been a very tragic year for the boxing world, but today we've truly lost one of its crown jewels," Lewis wrote on a blog on this website.
"I'm completely devastated by the passing of my long-time friend, mentor and trainer Emanuel 'Manny' Steward.
"Manny has helped me get through some of the biggest fights in my career and I only regret that I couldn't return the favour and see him through his biggest fight."
An inductee of the International Boxing Hall of Fame and the World Boxing Hall of Fame, Steward also worked for many years as part of HBO's commentary team on fights.
"There are no adequate words to describe the enormous degree of sadness and loss we feel at HBO Sports with the tragic passing of Manny Steward," Ken Hershman, president of HBO Sports, said in a statement.
"For more than a decade, Manny was a respected colleague who taught us so much not only about the sweet science but also about friendship and loyalty.
"His energy, enthusiasm and bright smile were a constant presence. Ten bells do not seem enough to mourn his passing."
- Sports & Recreation