 When Richard Cromwell succeeded his father, Pierrepont was an unobtrusive but powerful influence in directing the policy of the government, and after a short period of retirement on Richard's fall he was chosen, early in 1660, a member of the council of state but refused to take his seat when secluded members were readmitted to the Restored Rump.He was elected MP for Nottinghamshire in the Convention Parliament of 1660, and probably was instrumental in saving the lives of some of the parliamentary leaders.At the general election of 1661 he was defeated, and, spending the remainder of his life in retirement, he died in 1678.