John Ruaridh Grant Mackenzie, 5th Earl of Cromartie (born 12 June 1948) is a Scottish engineer and peer.

[1][2] He is the only child of Roderick Mackenzie, 4th Earl of Cromartie and his second wife, the former Olga (née Laurence) Mendoza (d.

[1] His mother, who was previously married to Peter Mendoza, was a daughter of Stuart Laurance of Paris.

[3] His paternal grandmother was Lady Sibell Lilian Mackenzie, suo jure Countess of Cromartie, who married his grandfather, Lt.-Col. Edward Walter Blunt later Blunt-Mackenzie DL (the eldest son of Maj.-Gen. Charles Harris Blunt of Adderbury Manor).

[1] Cromartie married firstly Helen Murray, daughter of John Murray, a steelworker at Lanarkshire, in 1973, and divorced in 1983, by whom he had an only son:[3] He married secondly Janet Clare Harley, daughter of Christopher James Harley of Strathpeffer, Ross-shire, in 1985.