He was the fourth son of nine surviving children born to William Keith, 6th Earl Marischal, and Lady Mary Erskine.

The Honours of Scotland had been placed at Dunnottar for safety during the Wars of the Three Kingdoms, and Robert Overton, commanding a force of the New Model Army besieged the Castle hoping to recover them.

While the regalia was smuggled out of the castle to be hidden at Kinneff Parish church, Keith boarded ship for France, and was captured on his return by the parliamentarians.

[3] He was created Knight Marischal of Scotland upon Charles II return, and in 1677 was created Earl of Kintore along with the subsidiary title of Lord Keith of Inverurie and Keith Hall, a reward for his part in preserving the Honours of Scotland in various hiding-places during the British Interregnum.

1641), 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).