Portrait of William, 1st Earl Cowper (d.1723), three-quarter-length, in Chancellor's robes, his right arm resting on a table on which lies the Purse of the Great Seal

The sitter was the son of Sir William Cowper, 2nd Bt. (d.1706) , Member of Parliament for Hertford (1679-81; and 1689-1700) and a leading Whig politician, and his wife Sarah, daughter of Sir Samuel Holled, a London merchant. His grandfather Sir William Cowper, 1st Bt., had been created a Baronet for his support of the Royalist cause during the civil war. In 1682 he entered the Middle Temple and in 1688, shortly before he was called to the Bar, he married Judith, daughter and heir of Sir Robert Booth, a London merchant. He attached himself to the home circuit, on which he obtained considerable practise, and he was appointed King's Counsel in 1694. In 1695 he was returned to Parliament as junior Member for Hertford and soon achieved a reputation as the finest speaker in the House. His practice as a barrister continued to prosper and in 1705 he succeeded Sir Nathan Wright as Lord Keeper. In 1706, shortly after his second marriage to Mary Clavering, he was created Baron Cowper and shortly afterwards was appointed Lord High Chancellor, an office he held until the defeat of the Whigs in 1710. He was later reappointed Lord Chancellor and then given an Earldom in 1718.