The National Museum of Ireland today consists of four separate museum buildings, three of which are situated in Dublin and one in Castlebar, Co. Mayo. The National Museum of Ireland - Archaeology and History is situated on Kildare Street, Dublin 2 and was the original home of the Dublin Museum of Science and Art which opened in 1890. The National Museum of Ireland - Decorative Arts and History, located at Collins Barracks, Benburb Street, Dublin 7, opened in 1997 and is the administrative headquarters of the National Museum of Ireland. The National Museum of Ireland - Natural History, Merrion Street, Dublin 2 belonged to the Royal Dublin Society (RDS) and has been open to the public since 1857. 

The most recent addition to the National Museum is the National Museum of Ireland Country Life, Turlough Park, Castlebar, Co. Mayo which opened in 2001. It is the first branch of the National Museum of Ireland to be located outside Dublin and is the first purpose-built museum to be constructed since the development of the Kildare Street building in the 1880's. The National Museum of Ireland is charged with preserving and making accessible the portable, natural and cultural material heritage of Ireland while responsible for communicating to both the people of Ireland and visitors an understanding of our heritage.

The museum also serves to deepen cultural ties both within Ireland and with other countries as well as opening a window on the world's material heritage through which Irish people may appreciate their own culture in its European and global context.