The Honourable William Cust (23 January 1787 – 3 March 1845), was a British barrister and Member of Parliament (MP). He also served as Commissioner of Customs. Cust was a younger son of Brownlow Cust, 1st Baron Brownlow, by Frances, daughter of Sir Henry Bankes, of Wimbledon. John Cust, 1st Earl Brownlow, Peregrine Cust, Rev. Henry Cockayne Cust and Sir Edward Cust, 1st Baronet were his brothers. He sat as Member of Parliament for Lincolnshire between 1816 and 1818 and for Clitheroe from 1818 to 1822, when he took the Chiltern Hundreds.