His publicist, Paul Shefrin, said said Williams died on Tuesday night at his US home following a year-long battle with bladder cancer.
Williams said in November 2011 that he was diagnosed with cancer but planned to continue performing.
Williams began singing with his brothers as a child, and his easy style and mellow voice led president Ronald Reagan to call him "a national treasure."
Although his version of Moon River made him world famous, it was among his many hits, including Butterfly and Can't Get Used To Losing You.
