Steward, who had recently undergone surgery for a stomach illness, died on Thursday night aged 68 with his family gathered at his hospital bedside.
Involved in the careers of over 40 champions, Steward established his reputation as one of boxing's greatest coaches at the legendary Kronk Gym in Detroit.
Among his extensive list of world title-holders was former undisputed heavyweight king Lewis, who he trained from 1995 until the end of his career in 2003.
"I'm completely devastated by the passing of my long-time friend, mentor and trainer Emanuel 'Manny' Steward," Lewis said on his official website.
"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.
"We've maintained a close relationship and the last time we spoke he seemed his usual upbeat self, so it was very disturbing to hear about his illness and rapid decline.
"Manny always told me I was the best, but the truth is, HE was the best and I'm grateful, privileged and honoured to be counted among his many historic successes.
"This has been a very tragic year for the boxing world, but today we've truly lost one of its crown jewels.
"Manny was giving, selfless, compassionate and stern. He always gave back to the community and never forgot where he came from.
"He was an institution unto himself and I'm proud to have had him in my corner for so many years."
Lewis and Steward shared a strong bond forged upon their mutual admiration.
When Lewis slumped to a shock second-round knockout defeat by Oliver McCall in 1994, Steward was recruited as coach and their 18-fight partnership saw Lewis claim the WBC, WBA and IBF belts.
One of Lewis' successors as world heavyweight champion, Wladimir Klitschko, was being trained by Steward for next month's showdown with Mariusz Wach.
"Boxing has suffered a tremendous loss with the passing of Emanuel Steward," Klitschko said.
"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.
"I will miss our time together. The long talks about boxing, the world, and life itself. Most of all I will miss our friendship."
Klitschko, who holds the IBF, WBA and WBO belts, vowed to achieve the targets set by Steward in honour of his mentor.
"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," he said.
"I know he will be with us in spirit along the way and we will accomplish these goals in his honour.
"Rest in peace Emanuel. You will be greatly missed. Until we meet again my friend."
Two of Britain's most respected trainers united in paying tribute to Steward, who was also a respected analyst for American cable network Home Box Office.
Enzo Calzaghe, father of former undisputed super-middleweight champion Joe, described him as "exceptional".
"It's usually fighters who make trainers, but he was unique in that he made fighters," he told BBC Radio 5 Live.
"When boxers went to him they were normal types of boxers, after he taught them they were champions.
"To say the least, Emanuel Steward was an exceptional trainer."
Steward masterminded Klitschko's wide points victory over David Haye in Hamburg last year and the Bermondsey fighter's own trainer, Adam Booth, said it was an honour to lose to him.
"He was up there with the best. It's a sad, sad day," Booth told Sky Sports News.
"He was not just a great coach, he trained fighters but also educated the boxers he worked with for decades.
"I grew up watching him and listening to him. No professional likes to lose but if you have to, it's an honour to lose to Manny Steward.
"In my career, I've never looked across at the other corner and been intimidated, except for last year."