He was born at Walcot, near Bath, Somerset,[1][2] the son of Commander John Guyon RN (1767–1844), a shipmate and friend of the Duke of Clarence (later William IV of Britain), and descended from a French noble family.

[3] After receiving a military education in England, Guyon fought against Dom Miguel in the Liberal Wars in Portugal.

Under the name of Kourshid Pasha, he, as a general of division, was Governor of Damascus, and at the beginning of the Crimean war, did much to organise the army of Kars.

[1][5] According to the Oxford Dictionary of National Biography he was "the first Christian to obtain the rank of pasha and a Turkish military command without being obliged to change his religion".

[citation needed] The 1863 Chambers Encyclopaedia states "Indomitable courage, and an incessant care for the comfort of the troops under his command, were the chief features in Guyon's character".