Sir Donald Macmaster, 1st Baronet, KC (3 September 1846 – 3 March 1922) was a Canadian lawyer and a politician in both Canada and the United Kingdom. Macmaster was born into a family of Scottish descent in Williamstown, Glengarry County, Canada West (now in eastern Ontario). He studied law at McGill University, was called to the Quebec bar in 1871, and set up practice in Montreal. Macmaster served as Crown Prosecutor for many cases. He was called to the Ontario bar and appointed Queen's Counsel in 1882.