Alastair Mackenzie (born 8 February 1970) is a Scottish actor. He was born in Trinafour, near Perth and educated at Westbourne House School and Glenalmond College in Perthshire.

Mackenzie left home at the age of 18 and moved to London. Best known as having played the young laird Archie MacDonald in the BBC drama Monarch of the Glen, he also has theatre and film credits to his name.

He lives in Islington with his partner, Scottish actress Susan Vidler, with whom he has two children: a daughter, Martha, born in December 1999 and a son, Freddie, born in September 2004. His brother is director David Mackenzie, with whom he co-founded Sigma Films.