In 1844 Pleydell-Bouverie was returned to Parliament for Kilmarnock Burghs, a constituency he represented until 1874. He served as Under-Secretary of State for the Home Department in Lord John Russell's first administration from July 1850 to March 1852, and from April 1853 to March 1855 he was Chairman of Committees of the House of Commons, while Lord Aberdeen was prime minister. In March 1855, when Lord Palmerston became premier, Pleydell-Bouverie was made Paymaster-General and Vice-President of the Board of Trade, and sworn of the Privy Council. In August of the same year he was transferred to the Presidency of the Poor Law Board, a position he held until 1858. However, he was never a member of the cabinet. In 1857 he was appointed one of the committee of the Council on Education. He was Second Church Estate Commissioner from August 1859 to November 1865, and from 1869 he was one of the Ecclesiastical Commissioners for England.