Vaughan succeeded his father as earl of Carbery in 1634 and joined the Irish House of Lords. Carbery was called to the bar by Gray's Inn in 1637 and did not sit in either the Short or Long Parliaments summoned in 1640. He maintained a low profile in politics, and at the outset of the Civil War, his loyalties were sufficiently ambiguous for him to be courted as a supporter by both King and Parliament. Parliament appointed him lord lieutenant of Carmarthenshire and Cardiganshire in February 1642 and assigned to him the task of executing the militia ordinance in those counties. Carbery instead declared for the king, and he and his uncle, Henry Vaughan, raised a regiment and marched to the support of the king at Oxford in January 1643. As a reward for his loyalty, on 4 April Charles appointed Carbery lieutenant-general of Carmarthenshire, Cardiganshire and Pembrokeshire and sent him to secure the counties for the king. This presented little difficulty in Carmarthenshire and Cardiganshire, as both were royalist leaning, but in Pembrokeshire the seaports of Tenby and Pembroke had active Parliamentarian sympathies. Carbery showed little appetite for a direct confrontation, and after securing an informal truce with the towns, settled down to await developments elsewhere.