Sir Joseph Williamson (1633-3 October 1701), English politician, was born at Bridekirk, near Cockermouth, his father, Joseph Williamson, being vicar of this place.

He was educated at St Bees, at Westminster School and at Queen's College, Oxford, of which he became a fellow, and in 1660 he entered the service of the Secretary of State, Sir Edward Nicholas, retaining his position under the succeeding secretary, Sir Henry Bennet, afterwards Earl of Arlington. He was involved with the foundation of the London Gazette in 1665. He entered parliament in 1669, and in 1672 was made one of the clerks of the council and a knight.

In 1673 and 1674 he represented his country at the Congress of Cologne, and in the latter year he became Secretary of State, having practically purchased this position from Arlington for £6000, a sum which he required from his successor when he left office in 1679. Just before his removal he had been arrested on a charge of sharing in the popish plots, but he had been at once released by order of Charles II.

After a period of comparative inactivity Sir Joseph represented England at the Congress of Nijmwegen in 1697, and in 1698 he signed the first treaty for the partition of the Spanish Monarchy. He died at Cobham, Kent, on 3 October 1701. Williamson was the second president of the Royal Society, but his main interests, after politics, were rather in antiquarian than in scientific matters. Taking advantage of the many opportunities of making money which his official position gave him, he became very rich. He left £6000 and his library to Queen's College, Oxford; £5000 to found a school at Rochester; and £2000 to Thetford. A great number of Williamson's letters, despatches, memoranda, etc., are among the English state papers.