Rex Williams (born 20 July 1933) is a retired English snooker player.
Williams was an excellent junior player, both of snooker and of billiards. His professional career initially coincided with a period of decline in snooker. In the 1960s, when the World Championship was run as challenge matches, he twice challenged John Pulman, in 1964 and 1965, but was unsuccessful both times.
He won the World Professional Billiards Championship seven times from 1968 to 1983, including a reign as champion from 1968 to 1980. He was less successful at snooker, although he did become the oldest player to reach a world ranking final when, at the age of 53, he lost to Jimmy White in the 1986 Rothmans Grand Prix Final.
Williams was heavily involved in the administration of snooker and billiards. In 1968 he inspired the resurrection of the defunct Professional Billiards Players Association as the World Professional Billiard and Snooker Association. He was chairman of the WPBSA from 1968 to 1987 and from 1997 to 1999.