The Merrion is located in houses built in the 1760's by Lord Monck (Charles Stanley Monck) for wealthy Irish merchants and nobility. He lived in No. 22, which became known as Monck House. The most important of the four houses is, however, No. 24 Upper Merrion Street. This was leased to Garrett Wellesley, Earl of Mornington, in 1769, it has since been known as Mornington House. The house is remembered historically as being the birthplace of Arthur Wellesley, the 1st Duke of Wellington.

All four houses had been in use as state offices for most of this century. The well-known Irish writer, Flan O'Brien, (also known as Myles na Gopaleen) author of "The Third Policeman", allegedly worked in the buildings when he worked for the government.

The Merrion houses a spectacular collection of 19th and 20th Century art which is widely considered to be one of the most important private collections in Ireland. The Merrion's grand interiors offer the perfect backdrop for the artworks, resulting in a dramatic and successful marriage of classical architecture and noteable Irish and European art.