Kilmainham's foundation dates to the early Christian period, with the monastery of Cell Maignenn (Cill Mhaighneann in modern Irish) established by the year 606.

[3] Viking cemeteries at the site of the monastery and at nearby Islandbridge were discovered during gravel quarrying, railroad works and the preparation of the War Memorial Gardens.

[7] Strongbow erected for them a castle about 2 kilometres or 1 mile distant from the Danish wall of old Dublin; and Hugh Tyrrel, first Baron Castleknock, granted them part of the lands which now form the Phoenix Park.

[8] Until the time of Queen Elizabeth, when Dublin Castle became the centre of English power, the Lord Lieutenants often held court at the manor of Kilmainham.

In 1559, Thomas Radclyffe, 3rd Earl of Sussex, on being again appointed Lord Lieutenant, found that the building at Kilmainham had been damaged by a storm, and had to hold court at the palace of St. Sepulchre.

The following year Elizabeth ordered that Dublin Castle be upgraded to enable the Lord Lieutenant to reside there, and Kilmainham fell out of favour.

Kilmainham is home to an important Viking Age burial site, part of a complex of cemeteries which also includes finds at the War Memorial Gardens.