Thomas Hamilton, 1st Earl of Haddington (1563 – 29 May 1637), designated before his peerage as 'of Drumcarny, Monkland, and Binning', was a Scottish administrator, Lord Advocate, judge, and Lord Lieutenant of Haddingtonshire.
The son of Sir Thomas Hamilton of Priestfield, a judge of the Court of Session as Lord Priestfield, by his first wife Elizabeth, daughter of James Heriot of Trabroun, Haddingtonshire, Thomas junior was educated in Paris.
He was admitted an Advocate in 1587, a Lord of Session in 1592, appointed Lord Advocate in 1596, Lord Clerk Register in 1612, and in 1616 became Lord President of the Court of Session.
He was on very friendly terms with James VI, his legal talents being useful to the king, and he was one of the eight men called the Octavians who were appointed to manage the finances of Scotland. Widely regarded as an able administrator, Hamilton was entrusted with a large share in the government of Scotland when James removed to London in 1603. In 1612 he was appointed Lord Clerk Register to the Privy Council to succeed Lord Curriehill. After the death of James VI the earl resigned his offices, but served Charles I as Keeper of the Privy Seal of Scotland. Thomas was referred familiarly to his friends as 'Tam o' the Cowgate', his Edinburgh residence being in that street.
On 19 November 1613, he was created a Lord of Parliament as Lord Binning. Further, on 20 March 1619, he was created Earl of Melrose. Upon the death of the first and last Viscount of Haddington (on 28 February 1626), the king agreed to exchange the title of Earl of Melrose to that of Earl of Haddington, with the original precedence and remainder to heirs male bearing the surname and Arms of Hamilton. In 1628 The Earl of Haddington purchased the Tyninghame estate for 200,000 merks.
The 1st Earl of Haddington married, (1) c. 1588, Margaret (d. Dec 1596), only child of James Borthwick of Newbyres, by whom he had two daughters. He remarried (2) in 1597, Margaret (d. 31 May 1609), daughter of James Foulis of Colinton, and had, with other issue:
- Thomas Hamilton, 2nd Earl of Haddington, a Covenanter, Governor of Dunglass Castle, and killed there in a massive explosion on 30 August 1640. Married, with issue.
- Sir John Hamilton of Trabroun (dvp). Married with issue who died young.
- Lady Jean Hamilton, who married John Kennedy, 6th Earl of Cassilis, and had issue, including Lady Margaret Burnet, who married c.1672 Gilbert Burnet, later Bishop of Salisbury.
The 1st Earl married again (3) on 3 September 1613, Julian (buried 30 March 1637), daughter of Sir Thomas Ker of Ferniehirst, and widow of Sir Patrick Hume of Polwarth, by whom he had another son:
- Robert Hamilton, born 14 May 1614 and killed in the explosion at Dunglass Castle on 30 August 1640, unmarried.