[2] Macdonald was also a Deputy Lieutenant of Inverness-shire and a brigadier-general in the Royal Company of Archers.

He succeeded his elder brother in the baronetcy in 1766 and in 1776 he was raised to the Peerage of Ireland as Baron Macdonald, of Slate in the County of Antrim.

[3] In 1778 he raised the Macdonald's Highlanders and was Brigadier-General in the Royal Company of Archers.

[2] On 3 May 1768 Lord Macdonald married Elizabeth Diana Bosville (1748–1789) at St Giles in the Fields, London.

[2] Through his daughter Diana, he was a grandfather of thirteen grandchildren, including Sir George Sinclair, 2nd Baronet, a writer and a MP for Caithness who married Lady Catherine Camilla Tollemache; John Sinclair, who became Archdeacon of Middlesex; Capt.