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. He subsequently again served as a staff officer with the French Army and is known to have been at Lauffeld in 1747, where Cumberland was defeated by Saxe, as well as with the force assembled for the 1759 planned French invasion of Britain.