Marchmont House lies on the east side of the small town of Greenlaw, and near the former village of Polwarth in Berwickshire, in the Scottish Borders area of Scotland. It is about five miles (8 km) 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.