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.