Denzil was the final Baron Holles, at which time the estates devolved on a cousin, John Holles (1662–1711), 4th Earl of Clare and Duke of Newcastle.
He was created Baron Haughton, of Haughton in the County of Nottingham, in 1616, and was made Earl of Clare in 1624.
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He was the son of the 2nd Earl of Ashburnham and the former Elizabeth Crowley, being styled Viscount St Asaph from birth, and was baptised on 29 January 1761 at St George's, Hanover Square, London, with King George III, the Duke of Newcastle and the Dowager Princess of Wales as his godparents.
Five days later the representatives of the elected delegates had an interview in London with the colonial secretary, the Duke of Newcastle, who informed them that it was now too late to discuss the question of the retention of British rule.
His first wife was Elizabeth Trevor, daughter of Thomas Trevor of Glynde, Sussex and his second wife was Gertrude Holles, sister of Thomas Holles, Duke of Newcastle.
The earl had five sons, one of whom became Henry Pierrepont, 1st Marquess of Dorchester, another was Francis Pierrepont (died 1659), a colonel in the parliamentary army and afterwards a member of the Long Parliament; and another was William Pierrepont (1608–1679), father-in-law of Gilbert Holles, 3rd Earl of Clare and also Henry Cavendish Duke of Newcastle upon Tyne.
His father died on 11 December 1757, leaving Theophilus just £50 in his will, and the following day Theophilus wrote to the Lord Chamberlain, the Duke of Newcastle, asking for work in a theatre.