Duncan McLennan (17 September 1861 – 21 May 1946) was an Australian politician.
He was born in Strathalbyn in South Australia to farmer Kenneth McLennan and Margaret McGregor.
The family moved to Ailsa in Victoria around 1873, and McLennan became a farmer in the area.
He moved to Geelong in 1910, where he was director of Federal Woollen Mills and from 1913 to 1937 Melbourne Harbour Trust commissioner.
He was closely involved with non-Labor politics as a founding chairman of the People's Party, and in 1917 was elected to the Victorian Legislative Assembly for Barwon for the Nationalist Party's Economy faction.