The barony was purchased under compulsion for £10,000 in 1625. The family had amassed great wealth by trading in tin and wool. Educated at Exeter College, Oxford, John Robartes fought on the side of the Parliament during the Civil War, being present at the Battle of Edgehill and at the First Battle of Newbury, and was a member of the committee of both kingdoms. He is said to have persuaded the Earl of Essex to make his ill-fated march into Cornwall in 1644; he escaped with the earl from Lostwithiel and was afterwards governor of Plymouth.
Between the execution of Charles I and the restoration of Charles II he took practically no part in public life, but after 1660 he became a prominent public man, owing his prominence partly to his influence among the Presbyterians, and ranged himself among Clarendon’s enemies. He was Lord Deputy of Ireland in 1660—1661 and was Lord Lieutenant in 1669—1670; from 1661 to 1673 he was Lord Privy Seal, and from 1679 to 1684 Lord President of the Council. In 1679 he was created Viscount Bodmin and Earl of Radnor, and he died at Chelsea on 17 July 1685.