Marchmont House lies on the east side of the village of Greenlaw, and near to a church in Polwarth in Berwickshire, in the Scottish Borders area of Scotland. It is about five miles south west of Duns, about 19 miles (31 km) west of Berwick-upon-Tweed and about 40 miles (64 km) south east of Edinburgh. Situated in a gently undulating landscape, the estate is intersected by Blackadder Water, and its tributary burns. With the Lammermuir Hills to the north and views towards the Cheviot Hills in the south, this part of Berwickshire, sometimes referred to as the Merse, is scenic and contains rich agricultural land.

Lord Polwarth, of Polwarth in the County of Berwick, is a title in the Peerage of Scotland. It was created in 1690 for Sir Patrick Hume of Polwarth, 2nd Baronet, Lord Chancellor of Scotland from 1696 to 1702. In 1697 he was further created Lord Polwarth, of Polwarth, Redbraes and Greenlaw, Viscount of Blasonberrie and Earl of Marchmont, also in the Peerage of Scotland. Upon the death of his grandson, the third Earl, the creations of 1697 became dormant (unclaimed).