William Nagy (21 February 1921–19 January 1973) was a Canadian actor, who lived and worked primarily in the United Kingdom.

Nagy was born in Budapest, Hungary in 1921. His family emigrated to Canada when he was a child, and he was brought up in Toronto. He originally trained as a ballroom dancer, and studied acting at the Actors Studio in New York City. He came to London in mid-1949 as Paul Muni's understudy in the first British production of Death of a Salesman. After the run ended, he chose to remain in England.

Nagy appeared in some 140 film and television roles between 1950 and 1973, typically as a token American or Canadian supporting character in British productions. In 1968 he appeared in The Trojan Tanker episode of the spy-fi series Department S. From 1967 to 1970, he played Gregg Flint on Coronation Street. His West End stage credits included "Stewpot" in South Pacific and Alvaro in The Rose Tattoo.

Nagy married actress Janet Macfarlane. Their daughter, Christina Nagy, was an actress.

Nagy died in London on 19 January 1973, at the age of 51.