Building work for a new courthouse commenced in late 1840 or early 1841.
The successful contractor, John Hanley, was already building the gaol and appears to have completed the work by 1844 as the Spring Assizes were held in the new courthouse in that year. The contract price was £6,000 for the courthouse building, and £1,000 for the portico. Funding came from the Commissioners of Public Works, who were reimbursed by the Grand Jury in whole or in part.
A refurbishment project was completed in 2006. It provides office accommodation for court staff, and a range of facilities for the legal profession, judges, members of the public (including those with accessibility issues), and others.
The most significant structural change was the removal of the original main staircase, which only linked the ground and first floor. It was replaced with a new staircase which links all floors open to the public and is located in a more central position.
Nenagh Courthouse is supported by Nenagh District Court Office.