Sir John William O'Sullivan (c. 1700 – c. 1760) was an Irish professional soldier, who spent most of his career in the service of France, but is best known for his involvement in the Jacobite rising of 1745, an attempt to regain the British throne for the exiled House of Stuart.

[2] Information on his early life is limited and taken from The Young Juba, an often unreliable biography of Charles Stuart written in 1748 by Aeneas MacDonald, using the pseudonym Michell.

[2] The Penal Laws limited opportunities for the Irish Catholic gentry and like many contemporaries, O'Sullivan was educated in Paris and Rome, possibly in preparation for the priesthood.

He started purchasing weapons in early 1745 while the French provided limited logistical support, much of it brokered by Lord Clare; O'Sullivan joined Charles's household in March.

The campaign got off to a poor start when the ship Elizabeth, carrying weapons and a force of Franco-Irish regulars, had to turn back after being intercepted and damaged by HMS Lion.

On arrival, nearly every single contact urged Charles to return to France; he persuaded enough to support him but was dependent on a small force mobilised by Donald Cameron of Lochiel and other Lochaber chiefs.

[7] Cavalryman Sir John MacDonald, another of the 'Seven Men', later wrote that Lochiel admitted to lacking military experience; he therefore suggested that although either he or Francis Strickland could do the job of organising the Jacobite forces, O'Sullivan was the best qualified.

[11] They preferred to consolidate their position and resented the exiles, many of whom held French commissions and would be treated as prisoners of war if the Rising failed; the Scots risked execution and loss of their lands.

The influence of this is particularly noticeable in Peter Watkins' 1964 Culloden, based on Prebble's work, which in the course of framing the Jacobites as a largely feudal, archaic army led by incompetent aristocrats, depicts O'Sullivan as a "complete fool".

[citation needed] O'Sullivan's reputation in France does not seem to have been impacted by the Jacobite defeat; he was included on a 'gratification list' drawn up by the French in October 1746 and offered the choice of a colonelcy in one of Clare's, Bulkeleys or Dillons regiments.