 
Sir William Duncan Geddis (9 July 1896 – 12 December 1971) was a unionist politician in Northern Ireland.
Geddis studied at Skerries College in Belfast before becoming a clothing manufacturer. He served in the Royal Army Ordnance Corps from 1940 to 1948, retiring with the rank of Major.
He was elected to the Belfast Corporation for the Ulster Unionist Party and served as Lord Mayor of Belfast from 1966 to 1969. He was knighted in 1969.