The actor, who turns 77 on Sunday (06Apr14), announced he would be leaving the programme in the middle of a live episode which aired in America on Monday (31Mar14).
He explained, "I've got this chronic back problem. But I've had a wonderful, brilliant, fantastic blast of a time... Pure joy. And I want to thank every one of you folks for your support."
Williams, who has also had two hip replacements, managed to make it through the first round of eliminations last week (24Mar14), despite struggling with the routines and earning the lowest scores among the contestants for two weeks in a row.
However, Williams insisted he has no regrets about signing up for the show, adding, "My time on Dancing With the Stars is an epic moment. This is something I'm going to carry with me."