In 845 the Vikings of Dublin attacked the site and the abbot of Terryglass, Aed son of Dub dá Chrích, was killed there.

[citation needed] When the Normans arrived in Ireland in the late 12th century, Dunamase became the most important Hiberno-Norman fortification in Laois.

MacMurrough gave Dunamase and his daughter Aoife in marriage to the Norman conqueror Strongbow in 1170 as part of a deal to enlist his help to regain his lands.

[citation needed] Later, with the marriage of Strongbow and Aoife's daughter and heir, Isabel, the castle passed into the hands of the Marshal family.

William Marshal, who later became Regent of England in the minority of Henry III, had five sons, all of whom succeeded him in turn and died without issue.

In the later 18th century Sir John Parnell started to build a banqueting hall within the ruins and this work incorporated medieval architectural details taken from other sites in the area.