Tristram Shandy by Laurence Sterne. Born in Clonmel in 1713, Sterne wrote the most unconventional novel of the eighteenth century — full of digressions, blank pages, marbled pages, and jokes about the impossibility of telling a story. Still radical. Still funny. It rewards rereading.
The Life of Laurence Sterne by Arthur Cash. The definitive two-volume biography, scholarly but readable, covers Sterne's Irish childhood and his years of fame in London and Paris. Volume one, covering his life up to the publication of Tristram Shandy, is the more relevant here.
The Siege of Clonmel — the historical background to the 1650 siege is covered in several general histories of the Cromwellian wars in Ireland, including Pádraig Lenihan's Confederate Catholics at War 1641–49 and John Barratt's Cromwell's Wars in Ireland.