Lewis has hosted the telethon since 1966 and he's been the MDA's national chairman since the early 1950s. He announced in May that he was retiring as host of the telethon, but he said he planned to make his final appearance on this year's Sept. 4 show.
The organization made the announcement Wednesday saying that Lewis "is a world-class humanitarian and we're forever grateful to him for his more than half century of generous service to MDA."
The group also said it will not be replacing Lewis as the national chairman.
No reason for the move was given, and Lewis has not commented.
Lewis, a Las Vegas resident, has in recent years battled a debilitating back condition, heart issues and the crippling lung disease pulmonary fibrosis.
MDA officials said more than $1 billion has been raised during Muscular Dystrophy Association telethons over the years and a national network of some 200 hospital-affiliated clinics has opened since Lewis became involved in the telethon.
The Associated Press contributed to this report.