During the Siege of Clonmel (1650), the old Manor Court was destroyed, and after the restoration of the 1st Duke of Ormonde's (1610–88) palatinate rights in 1662, he ordered the building of a new courthouse.

After that, the Clonmel Assizes was held in the building, and it was there that Father Nicholas Sheehy, the anti-Penal Laws agitator, was tried in 1766.

In the 1990s the Office of Public Works began to restore its original form and the open arcade of sandstone columns is once again a feature of the streetscape.

[10][11][12][13] The Main Guard is a formerly detached five-bay two-storey courthouse and market house, with arcaded ground floor.

[14][15] A major programme of restoration works, carried out to a design by Punch Consulting, commenced in 2004.