It was created in 1690 for Sir Patrick Hume of Polwarth, 2nd Baronet, Lord Chancellor of Scotland from 1696 to 1702 (the baronetcy had been created in the Baronetage of Nova Scotia in 1637 for his father and namesake Patrick Hume).

The claim to the lordship of 1690 was vested in his granddaughter, Anne Anstruther-Paterson (de jure 4th Lady Polwarth), daughter of Lady Anne Hume-Campbell, eldest daughter of the third Earl.

On her death the claim to the title passed to her aunt Diana Scott (de jure 5th Lady Polwarth), youngest daughter of the third Earl, and then to her son Hugh Hepburne-Scott.

The heirs apparent to the Earls of Marchmont used the courtesy title Lord Polwarth.

The other titles associated with the earldom derive from Greenlaw, four miles southwest of Polwarth, Redbraes Castle, the remains of which are immediately to the east of Marchmont House, and Blasonberry, which was located on the farm of Broomhill on the west bank of the Blackadder Water, quarter of a mile north of Greenlaw.