Earl of Haddington is a title in the Peerage of Scotland. It was created in 1627 for the noted Scottish lawyer and judge Thomas Hamilton, 1st Earl of Melrose. He was Lord President of the Court of Session from 1616 to 1625. Hamilton had already been created Lord Binning in 1613 and Lord Binning and Byres, in the County of Haddington, and Earl of Melrose, in the County of Roxburgh, in 1619. These titles were also in the Peerage of Scotland. The title of the earldom derived from the fact that he was in possession of much of the lands of the former Melrose Abbey. However, Hamilton was unhappy with this title and wished to replace it with "Haddington" (a title which was then held by John Ramsay, 1st Earl of Holderness and 1st Viscount of Haddington, but on whose death in 1626 both peerages became extinct). In 1627 he relinquished the earldom of Melrose and was instead created Earl of Haddington, with the precedence of 1619 and with limitation to his heirs male bearing the surname of Hamilton. This derived from the fact that he considered it a greater honour to take his title from a county rather than from an abbey. Hamilton was a member of the prominent Scottish family of that name and descended from John de Hamilton, younger son of Walter de Hamilton (or Walter Fitzgilbert), who was granted the feudal barony of Cadzow and who is also the ancestor of the Dukes of Hamilton and Dukes of Abercorn.
Lord Haddington was succeeded by his eldest son, the second Earl. He was a staunch Covenanter. Haddington served as Governor of the Castle of Dunglass, and was killed by a massive explosion there in 1640. His eldest son, the third Earl, died childless at an early age and was succeeded by his younger brother, the fourth Earl. On his death the titles passed to his son, the fifth Earl. He married Margaret Leslie, 8th Countess of Rothes (d. 1700), daughter of the noted statesman John Leslie, 1st Duke of Rothes, who had received a re-grant of the earldom of Rothes in 1663 which allowed it to be passed on to his daughter (see the Earl of Rothes for earlier history of this title). According to the regrant of 1663, the earldom of Rothes was not allowed to be united with the earldom of Haddington. The couple were therefore in 1689 granted a patent of the marriage contract, which stated that the earldom of Rothes should descend to their eldest son, the Hon. John, while the earldom of Haddington should be inherited by their second son, the Hon. Thomas. According to this patent Lady Rothes was succeeded by her eldest son John, the ninth Earl (who assumed the surname of Leslie; see the Earl of Rothes for further history of this branch of the family).
Lord Haddington was succeeded accordingly by his second son Thomas, the sixth Earl. He obtained a new charter of the earldom. He sat in the House of Lords as a Scottish Representative Peer from 1716 to 1735 and served as Lord-Lieutenant of Haddingtonshire from 1716 to 1735. He was also appointed Hereditary Keeper of Holyrood Palace. His eldest son Charles Hamilton, Lord Binning, married Rachel (d. 1773), daughter of George Baillie, of Mellerstain House and Jerviswood. Through this marriage Mellerstein House and the Jerviswood estate came into the Hamilton family. Lord Binning predeceased his father. Lord Haddington was therefore succeeded by his grandson, Thomas the seventh Earl (the eldest son of Lord Binning), who married Mary Lloyd, née Holt (great-niece of Sir John Holt, Lord Chief Justice 1689-1709). On his death the titles passed to his son Charles, the eighth Earl. He was a Scottish Representative Peer from 1807 to 1812 and Lord-Lieutenant of Haddingtonshire from 1804 to 1823. He was succeeded by his son, the ninth Earl. He was a Tory politician and served as Lord-Lieutenant of Ireland from 1834 to 1835 and as First Lord of the Admiralty (with a seat in the cabinet) from 1841 to 1846. In 1827, one year before he succeeded his father in the earldom, he was created Baron Melros, of Tyninghame in the County of Haddington, in the Peerage of the United Kingdom.
Lord Haddington resigned the office of Hereditary Keeper of Holyrood Park in 1843 for a compensation fee of £40,000. He was childless and on his death in 1859 the barony of Melros became extinct.
The ninth Earl was succeeded in the Scottish titles by his second cousin, the tenth Earl. He was the son of George Baillie of Jerviswood (who had assumed the surname of Baillie in lieu of Hamilton), son of the Hon. George Hamilton, younger brother of the seventh Earl. He assumed in 1859 by Royal licence the additional surname of Hamilton to that of Baillie. Lord Haddington was a Scottish Representative Peer in the House of Lords from 1859 to 1870 and served as a government whip in the 1866–1868 Conservative administration. On his death the titles passed to his son, the eleventh Earl. He was Lord-Lieutenant of Haddingtonshire from 1876 to 1917. In 1858 Haddington assumed by Royal licence the additional surname of Arden after that of Baillie-Hamilton. His eldest son George Baillie-Hamilton, Lord Binning (1856–1917), was a Brigadier-General in the Army. However, he predeceased his father. Lord Haddington was therefore succeeded by his grandson, the twelfth Earl. He was the son of Lord Binning. He sat in the House of Lords as a Scottish Representative Peer from 1922 to 1963 (when all Scottish peers were granted the right to sit in the House of Lords) and served as Lord-Lieutenant of Berwickshire from 1952 to 1969. He was succeeded by his only son, the thirteenth Earl (1941–2016), in 1986. As of 2017 the titles are held by his only son, the fourteenth Earl, who succeeded in 2016.
Several other members of the Baillie-Hamilton family have also gained distinction. George Baillie, son of the Hon. George Hamilton, younger brother of the seventh Earl, sat as Member of Parliament for Berwickshire. He was the father of (apart from the tenth Earl) 1) the politician and judge Charles Baillie, Lord Jerviswoode and 2) Reverend the Hon. John Baillie (1810–1888), Canon Residentiary of York, who the great-grandfather of John Robert Edward Baillie, a Brigadier in the Royal Engineers. The Venerable Charles Baillie-Hamilton (1764–1820), son of the Hon. George Hamilton, younger brother of the seventh Earl, was Archdeacon of Cleveland. He was the father of Charles John Baillie-Hamilton, a Member of Parliament, and William Alexander Baillie-Hamilton (1803–1881), an Admiral in the Royal Navy.
The family seat now is Mellerstain House, near Kelso, Berwickshire. The former family seat was Tyninghame House, near Tyninghame, East Lothian.