William Martin Smyth (born 15 June 1931) is a Northern Irish unionist politician, who served as the Ulster Unionist Party (UUP) Member of Parliament (MP) for Belfast South from 1982 to 2005. He was a vice-president of the Conservative Monday Club. He is also an ordained minister of the Presbyterian Church in Ireland and was minister of Raffrey, County Down from 1957 to 1963 and of Alexandra Church, Belfast 1963–1982.