Marlborough House is a mansion in Westminster, London. It was built for Sarah, Duchess of Marlborough, a close friend of Queen Anne. The Duchess wanted her new house to be "strong, plain and convenient". Designed by Christopher Wren, both father and son, the building was completed in 1711.

In the 19th century the house was substantially enlarged and used by members of the Royal Family. From 1863 until he became King Edward VII in 1901, it was the home of the Prince and Princess of Wales. During this period Marlborough House became the social centre of London.

An Art Nouveau memorial in the Marlborough Road wall of the house commemorates Alexandra, Edward's queen.

Today the building houses the Commonwealth Secretariat.