William Westwater was born in Scotland in 1922. His father, Willie Westwater senior, was a member of the Dunipace Juniors Football Club that won the Scottish Junior Cup in the 1905-1906 season.
Willie junior started his soccer career with Perth junior club Jeanfield Swifts. During the war period he had several offers to join professional clubs. In November 1941 Willie had a trial with Falkirk. In August 1942 he had a trial with Dundee United and played in one game in the North Eastern Football League. In January 1943 both Rangers and Raith Rovers were said to be interested in signing him. He also represented the Scottish Command in exhibition games.
Willie played in 20 North Eastern Football League games for Dundee in the 1944-45 season and in two games at the start of the 1945-46 Southern Football League season. Later in the 1945-46 season he joined Greenock Morton.
The 5 feet 9 inches and 11 stone player remained with Morton until the end of the 1952-53 season when he was given a free transfer. While playing for Morton in the Scottish League he worked as a bricklayer in Perth.
On August 6, 1953, Willie Signed for Dundee United. In January 1954 it was announced that Willie would be emigrating to Canada. He played in three Scottish League games for United in the 1953-54 season.
In Canada Willie first joined Hamilton British Imperials.
In May 1954 he joined Brantford City.
Willie played at right back for Hamilton & District All Stars against Glasgow Rangers on May 19, 1954.
On May 18, 1955 Willie played for the Hamilton & District All-Stars against Huddersfield Town.