The first creation in the Scots Peerage came in 1580 in favour of Esme Stewart, 1st Earl of Lennox, who was created Duke of Lennox at the same time. See the latter title for more information on this creation of the earldom. The title of Lord Darnley had previously been held by John Stewart, head of the house of Stewart of Darnley and first Earl of Lennox (1488). The second creation in the Peerage of Scotland came in 1675 in favour of Charles Lennox, 1st Duke of Richmond. He was made Duke of Lennox at the same time. For more information on this creation, see the Duke of Richmond.
The only creation in the Peerage of Ireland was in 1725 to John Bligh, 1st Earl of Darnley, descended from a prominent Devon family via a cadet branch which had settled in County Meath, Ireland; he was the son of the Rt Hon Thomas Bligh who was in turn the son of John Bligh, of Plymouth, a Commissioner of Customs and Excise despatched to Ireland in search of forfeited estates, and in turn his father was William Bligh, a prosperous Plymouth merchant.
John Bligh, 1st Earl of Darnley, married Theodosia Hyde, 10th Baroness Clifton (of Leighton Bromswold), great-granddaughter of Lord George Stuart, younger son of Esmé Stewart, 3rd Duke of Lennox, also 3rd Earl of Darnley (see the Baron Clifton of Leighton Bromswold and the Duke of Lennox for earlier history of these titles). He represented Athboy in the Irish House of Commons from 1709 to 1721. In 1721 he was raised to the Peerage of Ireland as Baron Clifton of Rathmore, in the County of Meath. In 1723 the Darnley title held by his wife's ancestors (which had become extinct on the death of Charles Stewart, 6th Duke of Lennox and 6th Earl of Darnley in 1672) was revived when he was created Viscount Darnley, of Athboy in the County of Meath, in the Peerage of Ireland. In 1725 Bligh was further honoured when he was advanced as Earl of Darnley, in the County of Meath, also in the Peerage of Ireland. He was succeeded by his eldest son, the second Earl. He had already succeeded his mother in 1722 as eleventh Baron Clifton of Leighton Bromswold in the Peerage of England. Lord Darnley served as a Lord of the Bedchamber to Frederick, Prince of Wales, but died unmarried in 1747, aged 31.
He was succeeded by his younger brother, the third Earl. He had earlier represented Athboy in the Irish House of Commons and Maidstone in the British House of Commons. On his death the titles passed to his eldest son, the fourth Earl. In 1828 he presented a claim as heir-general to the dukedom of Lennox, but the House of Lords did not come to any decision on the matter. He was succeeded by his second but eldest surviving son, the fifth Earl. He was elected as Member of Parliament for Canterbury and served as Lord Lieutenant of County Meath. On the death of his grandson, the seventh Earl (who had succeeded his father in 1896), the barony of Clifford of Leighton Bromswold separated from the Irish titles when it devolved upon the late Earl's daughter and only child, the ten-month-old Lady Elizabeth Bligh, who became the seventeenth holder of the barony by writ of summons. Lord Darnley was succeeded in the Irish titles by his younger brother, the eighth Earl. A talented and successful cricketer who captained MCC, he sat in the House of Lords as an Irish Representative Peer from 1905 to 1927. On his death the titles passed to his only son, the ninth Earl. In 1937 he succeeded his first cousin The Lady Clifton (who died unmarried) in her ancient English barony by writ of summons being her heir-general, as eighteenth Baron Clifton of Leighton Bromswold. He was by his only son from his third marriage with Rosemary, Dowager Countess of Darnley (née Potter, died 2005), the eleventh Earl, who succeeded his half-brother (the only son from the first marriage of the ninth Earl), in 1980. As of 2017 the title is held by his only son, the twelfth earl, who succeeded his father in that year.
Several other members of the Bligh family have also attained distinction. Thomas Bligh (1654–1710), father of the first Earl, represented County Meath as its MP in the Irish Parliament and was sworn of the Irish Privy Council. Thomas Bligh, younger brother of the first Earl, was a general in the British Army and represented Athboy in the Irish House of Commons for sixty years. The Very Reverend Robert Bligh (c. 1704–1778), another younger brother of the first Earl, was an Anglican clergyman who became Dean of Elphin. General the Hon. Edward Bligh (1769–1840), second son of the third Earl, was a general in the British Army. The Hon. William Bligh (1775–1845), third son of the third Earl, was a colonel in the Army. The Hon. Sir John Bligh (1798–1872), fourth son of the fourth Earl, was a diplomat and served as Envoy Extraordinary and Minister Plenipotentiary to Hanover. Susan Bligh, Countess of Darnley, the eleventh Earl's wife was appointed Lord Lieutenant of Herefordshire in 2008.
The heir apparent is the present holder's eldest son Harry Robert Stuart Bligh, Lord Clifton (b. 1999)