Mellerstain House is a stately home around 13 kilometres north of Kelso in the Borders, Scotland. It is currently the home of the 13th Earl of Haddington.
Mellerstain was built between 1725 and 1778. The architect William Adam initially designed the east and west wings for George Baillie and Lady Grisel Baillie. Work ceased after the wings were completed,and it was another 45 years before George Hamilton commissioned Robert Adam to design and build the main mansion house. Hamilton was a son of the Earl of Haddington, and he inherited the Mellerstain estate when Lady Grisel Baillie died, changing his name to Baillie as a mark of respect.
The mansion house is possibly the only remaining complete building designed by Robert Adam, as most of his other works were additions to existing buildings.