He was born in France, the eldest son of Charles Gerard, Baron Brandon (later 1st Earl of Macclesfield), and Jeanne, the daughter of Pierre de Civelle, equerry to Queen Henrietta Maria.
[3] Having become a major-general in 1694, Macclesfield saw some service abroad, and in 1701 he was selected the first commissioner for the investiture of the elector of Hanover (afterwards King George I) with the order of the Garter, on which occasion he also was charged to present a copy of the Act of Settlement to the dowager electress Sophia.
James Douglas, 4th Duke of Hamilton also had a claim on the estate through his second wife Elizabeth Gerard, who was also a granddaughter of the 1st Earl.
It seems that Macclesfield preferred Mohun, a former captain of horse in his regiment, over Hamilton whom he disliked because of his Tory sympathies.
After over a decade of legal dispute, the pair fought their famous duel in Hyde Park, which resulted in the deaths of both men.