The sitter was the only son of Robert Knight (1675-1744), financier, and his first wife, Martha, née Powell (c.1681-1718). He was educated at Wadham College, Oxford, matriculating on 22 June 1719, and enrolled at the Inner Temple later that same year. His first wife, whom he married on 10 June 1727, was Henrietta St John (1699-1756), daughter of Henry St John, first Viscount St John, and his second wife, Angelica Magdalen Pellisary, and also half-sister to Henry St John, first Viscount Bolingbroke. Upon the death of his father in 1744 he inherited his estate at Luxborough, and was able to use his fortune to secure his elevation to Baron Luxborough on 8 August 1745. On 18 June 1756, he married for a second time, to Mary (d. 1795), the widow of Sir John Le Quesne (d. 1741), an alderman of London. In May 1763 he rose yet again in the peerage, taking the title of Earl of Catherlough. He died on 30 March 1772, leaving a wife and four children, the eldest of which, Robert, inherited the bulk of his estate.