He was the only son born to John Keith, 1st Earl of Kintore and the former Lady Margaret Hamilton.

His two sisters were Lady Jean Keith (the wife of Sir William Forbes, 4th Baronet of Monymusk)[1] and Lady Margaret Keith (the wife of Maj. Gavin Hamilton of Raploch).

[2] His paternal grandparents were William Keith, 6th Earl Marischal, and Lady Mary Erskine (the eldest daughter of John Erskine, 19th and de jure 2nd Earl of Mar and, his second wife, Marie Stewart, the daughter of Esmé Stewart, 1st Duke of Lennox).

[4] His mother was the only child, born posthumously, of Thomas Hamilton, 2nd Earl of Haddington by his second wife Lady Jean Gordon (the third daughter of George Gordon, 2nd Marquess of Huntly and Lady Anne Campbell, herself a daughter of Archibald Campbell, 7th Earl of Argyll).

Lord Kintore was a Tory and a Jacobite, and took part in the 1715 rising fighting at the Battle of Sheriffmuir.