Alastair Duncan may refer to:
Alastair Duncan (actor, born 1926) (1926–2005), English/Australian actor Alastair Duncan (Scottish actor), Scottish actor Alastair Duncan (British Army officer) (1952–2016), British Army general Alastair Duncan (wrestler), Scottish medallist at the 1958 Commonwealth Games
See also Alasdair Duncan (born 1982), Australian author and journalist