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 represented Glengarry in the Legislative Assembly of Ontario from 1879 to 1882 and in the House of Commons of Canada as a Conservative member from 1883 to 1887, when he lost his seat.

In 1905, Macmaster emigrated to the United Kingdom and settled in London, intending to practise in Privy Council cases, in which he already had considerable experience.

Having been defeated at Leigh in 1906, in 1910 he was elected to the House of Commons as Conservative member for the Chertsey division of Surrey, holding the seat until his death.