Earl of Darnley is a hereditary title that has been created three times, twice in the Peerage of Scotland and once in the Peerage of Ireland.
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.