Hewitt’s father was a member of the Coventry corporation, and in 1744 mayor. Hewitt was articled to an attorney before being called to the bar. He contested Coventry in 1754; and in 1761, as corporation candidate and with the support of the Archer interest, came out head of the poll.
He appears in Fox’s list of Members favourable to the peace preliminaries, December 1762, and in autumn 1763 was classed by Jenkinson as ‘pro’. But over Wilkes and general warrants he turned against the Government; and became one of the most frequent Opposition speakers on a pre-eminently legal subject. According to Walpole,
When the Rockingham Administration was being formed, Hewitt wrote to Newcastle:
Serjeant Hewitt, who has nothing to ask of Government for himself and who had never received any beneficial mark of public favour, begs leave to recommend his brother, Mr. William Hewitt, for something at home or abroad which may carry some public mark of respect to the Serjeant and therein do him credit.
William Hewitt was appointed a commissioner for the sale of ceded lands in the West Indies.
In February 1765 Hewitt had been one of the few who had spoken against the introduction of the Stamp Act; a year later he also opposed the Declaratory Act. Contemporaries said that it was his support of Chatham’s American policy which induced Camden, then lord chancellor, to appoint him a judge. On 20 Oct. 1767 Camden, when asked to advise on candidates for the post of lord chancellor of Ireland, wrote to Grafton about Hewitt:
Yet it proved to be no bad one. John Hely Hutchinson, an ambitious Irish lawyer and politician who rarely spoke well of anyone, wrote to W. G. Hamilton, in 1773:
In answer to your question about the chancellor ... he does his business very ably and expeditiously and to the general satisfaction of suitors and practisers in this country where he is much respected and a very popular character, and is in his private and public deportment a most worthy, honest and amiable man.
He died 28 Apr. 1789.