An Grianán Theatre, with a seating capacity of 383, is the largest theatre in Letterkenny and in the whole of County Donegal. It is located on Port Road in Letterkenny, across from The Oak Tree restaurant. It is run by Patricia McBride. It also boasts the largest stage in Ireland. An Grianán Theatre opened in October 1999. Magic of the Musicals was the first show performed on the An Grianán stage.
Each year it is used as a venue for the major local festivals including the Earagail Arts Festival and the Smithwick's Comedy on Tap festival, which in 2006 saw such comedians as Karl Spain, Jason Byrne, PJ Gallagher, Patrick McDonnell and Hector take to the An Grianán stage. It was also used to host the Fleadh Cheoil na hÉireann, in the summers of 2005 and 2006. It hosted the Pan Celtic Festival in 2007.