Mackenzie was the eldest son of William Mackenzie, 5th Earl of Seaforth (died 1740) by his wife Mary, only daughter and heiress of Nicholas Kennet of Coxhow [Coxhoe in Kelloe parish, County Durham[2]].
His father had taken part in the Jacobite rising of 1715 and had forfeited his estates and title under the Act of Attainder of 1716.
[3] He died in London on 18 October 1761 and was buried in Westminster Abbey.
[3] Mackenzie married (11 September 1741) Mary, eldest daughter of Alexander Stewart, 6th Earl of Galloway.
She died on 10 April 1751 and is buried at St Mary Abbots Church, Kensington.