William Armstrong (born 21 June 1943) is an Ulster Unionist politician in Northern Ireland. He served as Assembly Member for Mid Ulster from 1998 until 2011, when he was succeeded by his daughter, Sandra Overend. He was a member of the Agriculture and Rural Development Committee, the Committee for Enterprise, Trade & Industry and the Committee of the Environment. In 2005, he became the first Ulster Unionist candidate since 1983 to contest Mid Ulster in the Westminster General Election.