Statesman and politician. The son of John Hay, 8th Lord of Yester (1593 - 1653), who became the Earl of Tweeddale in 1646, Hay was a remarkable survivor in stormy times. Initially fighting for Charles I, he became a Covenanter but later returned to a Royalist. He served Cromwell and later Kings Charles II, James VII and William III, becoming Lord Chancellor of Scotland. Created the Marquess of Tweeddale in 1694, he conducted the inquiry into the massacre at Glencoe (1695). He was put in charge of the Scottish expedition to Central America (the Darien Scheme) which intended to establish a Scottish colony and trade links, and became the scape-goat when it collapsed following disease and mis-management losing the Scottish treasury a fortune.
He died in Edinburgh and was interred on the family estate at Yester.