He supported the parliamentarians against the republican or army party, and appears to have been one of the members excluded in 1648. He sat in Richard Cromwell's parliament for Member of Parliament for Dublin City, and endeavoured to take his seat in the restored Rump Parliament of 1659. He was made President of the Council of State in February 1660, and in the Convention Parliament sat for Carmarthen. The anarchy of the last months of The Protectorate converted him to royalism, and he showed great activity in bringing about the English Restoration. He used his influence in moderating measures of revenge and violence, and while sitting in judgement on the regicides was on the side of leniency. He was sworn of the Privy Council on 1 June and in November he succeeded his father as Viscount Valentia in the Irish peerage. On 20 April 1661, he was created Baron Annesley, of Newport Pagnell in Buckinghamshire and Earl of Anglesey in the Peerage of England.