Both states are members of the Council of Europe, the European Union, the Eurozone and the Organisation for Economic Co-operation and Development.

The first awareness and contact between both nations was through stories about Celtic migration from Iberia to Ireland as mentioned in the Lebor Gabála Érenn regarding the Milesians.

[1] In the mythical genealogies of the Gaels of Ireland, they all trace their ancestry back in the male line to Míl Espáine ("Soldier of Hispania").

[1] In 1554-58 Philip Prince of Asturias was married to Mary I and was named as titular King of Ireland in the Papal Bull Ilius ad quem.

Many Irishmen in rebellion against English rule subsequently sought refuge in Spain following the Flight of the Earls (1607), and for the next two centuries Irish soldiers contributed to Spanish Army of Flanders and fought side by side during the Dutch Revolts and during the Thirty Years' War.

[3] During the Anglo-Spanish War (1625–1630), proposals were made in 1627 to launch an invasion of Ireland under Shane O'Neill and Hugh O'Donnell but did not go further than the planning stage.

[8] At the same time, 250 Irish socialist volunteers joined the International Brigades and fought for the Spanish Republican faction.

By the summer of 1937, the Irish Brigade was "disarmed and ordered out of Spain by Franco" (Fearghal McGarry);[8] most of the socialists stayed until late 1938, although they were frequently treated as pariahs on their return home, and many emigrated to the UK.

[8] After the war ended in 1939, the Irish Minister presented his credentials in Burgos and formally recognized the new Spanish government under General Franco.

Recently, in January 2017, Irish Taoiseach Enda Kenny paid a visit to Spain,[12] and in 2024, in the context of the Israel-Hamas war, Prime Minister Pedro Sánchez visited Taoiseach Simon Harris in Dublin to discuss support for Palestinian statehood.