William Molesworth, the son of Sir Arscott-Ourry Molesworth, was born in Upper Brook Street, London, on 23rd May, 1810. Molesworth was disfigured in childhood by scrofula and this resulted in considerable teasing about his looks while at boarding-school.
Molesworth studied at Edinburgh University (1824-27) and Cambridge University (1827-28). After quarrelling with his mathematics tutor Molesworth left for Germany. This dispute eventually resulted in a duel, but neither man was hurt.
Influenced by the religious and political ideas of Jeremy Bentham and James Mill, Molesworth became involved in the campaign for parliamentary reform. In the 1832 General Election, Molesworth was elected to represent East Cornwall.
In 1834 Molesworth and John Stuart Mill founded the Radical journal, The London Review. Two years later, the two men purchased the Westminster Review and merged the two journals. Over the next few years the journal gave its support to radical politicians such as Thomas Wakley, Joseph Brotherton, Thomas Duncombe and Thomas Attwood, who were advocating further reform of the House of Commons.
Interested in the subject of penal reform, Molesworth wrote an influential report in 1837 condemning the system of transportation. He attacked this measures for many years and contributed to its ultimate abandonment. He also supported all measures for colonial self-government and favoured religious toleration and called for "complete religious liberty and equality and the removal of the disabilities of the Jews".
Molesworth's radical views made him unpopular with his wealthy, landowning constituents, and in 1837 was forced to seek a seat in a more progressive area. In July, 1837, he was elected with Edward Baines to represent Leeds. However, his decision to hold a peace meeting during the dispute with France, lost him the support of the voters and he decided not to stand in the 1840 General Election.
Molesworth returned to the House of Commons in September, 1845, when he defeated the Tory Party candidate in Southwark. He supported the Whig government of Lord John Russell and when the Earl of Aberdeen became prime minister in 1853, he appointed Molesworth as his Commissioner of the Board Works.