Thomas Osborne, 1st Earl of Danby (1631-1712), who was later created Marquis of Camarthen and then 1st Duke of Leeds, was the son of Sir Edward Osborne (d.1647) of Kiveton, Yorkshire, an ally of Lord Strafford's and a staunch royalist, and his second wife, Anne, widow of William Midelton, of Stockeld, Yorkshire, and daughter of Thomas Walmesley of Dunkenhalgh, Lancashire.
Thomas Osborne was brought up largely at Kiveton and succeeded in the baronetcy and to the family estates on his father's death, his elder half-brother having been killed in an accident in 1638. In the 1650s he came under the influence of his neighbour George Villiers, 2nd Duke of Buckingham, who brought him to Court following the Restoration where he identified himself closely with the interests of his patron. It was Buckingham who was to suggest to King Charles II that Osborne should succeed Arthur Annesley, 1st Earl of Anglesey, as Treasurer of the Navy, jointly with Sir Thomas Lyttleton, in 1668, and three years later he became sole Treasurer of the Navy. In 1673 Buckingham was again instrumental in arranging for him to succeed Clifford as Lord High Treasurer of England and Chief Minister to King Charles II, after which he was raised to the peerage as Baron Osborne. The following year he was raised to an earldom, styling himself Earl of Danby, and was appointed Lord Lieutenant of the West Riding of Yorkshire. He was made a Knight of the Garter in 1677 and between 1673 and 1678, while High Treasurer, the government of the country was effectively in his hands. However, his opponents in Parliament, chief among them Ralph Montagu, later Duke of Montagu, managed eventually to outmanoeuvre him and the exposure of his secret negotiations with France, although conducted with the King's approval, led to his impeachment and committal to the Tower of London from 1679-84. After his release he found himself in opposition to the government on account of his protestantism and his consequent distrust of King James II, and he gave his support to the pretensions of William of Orange and Mary to the English Crown, and was one of the seven conspirators to sign the invitation to William. His support was richly rewarded and his star was once more in the ascendant; he was made Marquis of Camarthen in 1689, and became Lord Lieutenant of the West Riding in Yorkshire and later all three Ridings. He failed, however, to reclaim the office of Treasurer which he coveted, although he was made President of the King's Council (1689) and his influence with William and Mary was such that by 1690 he was effectively prime minister. When William left for Ireland in June 1690, Camarthen was chosen, along with eight others to advise Queen Mary and was nominated her chief adviser. However, by the time that he was created Duke of Leeds, in 1694, his influence had once again been undermined by the concerted efforts of his Whig opponents and in the opening years of the 18th Century his influence on government was much diminished. He died of 'convulsions' in 1712. He had married Lady Bridget Bertie, second daughter of Montagu, Lord Willoughby D'Eresby, Earl of Lindsey, in 1654, and was succeeded by his son Peregrine, as 2nd Duke of Leeds.
This portrait is Lely's original prototype image of the sitter which Beckett dates to circa 1675 (R. Beckett, op. cit.). The portrait can be dated with some certainty as the sitter is shown as Lord High Treasurer, which he became in 1673, but is not shown in Garter robes so that it must predate his investiture with the Garter in 1677. A studio version of this type, with an inscription dating it to 1680, in which the sitter is shown without his wand of office, is in the National Portrait Gallery, London (Complete Illustrated Catalogue 1856-1979, London, 1981, p. 339, no. 1472). The Duke was also portrayed by Sir Godfrey Kneller as Lord High Treasurer, in Garter robes, circa 1685, in both full-length and half-length format (Department of the Environment, Chiswick House, and Holkham; see J. Douglas Stewart, Sir Godfrey Kneller and the English Baroque, Oxford, 1983, nos. 423-4). A later full-length portrait of the Duke, also in Garter robes and with his wand of office by Kerseboom and Van de Vaart, signed and dated 1705, is also in the National Portrait Gallery, London (purchased 1983).