Besides numerous research papers on the philology of multiple Celtic languages, he is the author of Medieval Welsh Literature and The Origins of the "Four Branches of the Mabinogi". He is also co-author with Professor Richard Coates of Celtic Voices, English Places. Breeze has written about Mabinogi studies, and The Mabinogion research, especially addressing historical and political parallels. In 1997 he published the controversial 'Did a woman write the Four Branches of the Mabinogi?', proposing a woman composer for this leading literature of British/ Welsh heritage. Breeze's theory rests on the unusual lack of warlike or fighting heroics compared to preceding literature; the high quantity of material on mothering, besides complex, in depth portraits of Mabinogi women. This much has been supported or tolerated by some scholars, but there has been discussion regarding Breeze's preferred candidate Gwenllian ferch Gruffydd. Since the 1997 article Breeze has provided further publications on this topic. In 2015, he published "The Historical Arthur and Sixth-Century Scotland", which locates King Arthur's battles from the 9th-century Historia Brittonum, placing them all in Scotland and Northern England, with the exception of Mount Badon in the year 493, located at a hillfort east of Braydon Forest, Wiltshire, but having nothing to do with Arthur. Using these identifications, he suggested that Arthur was a Briton from the Kingdom of Strathclyde who fought other Britons, rather than Anglo-Saxons. Other scholars have questioned his findings, which they believe are based on coincidental resemblances between place-names. Nicholas Higham comments that it is difficult to justify identifying Arthur as the leader in northern battles listed in the Historia Brittonum, but rejecting the implication in the same work that they were fought against Anglo-Saxons, and that there is no textual justification for separating Badon from the other battles. Andrew Breeze's British Battles 493-937: Mount Badon to Brunanburh was published in 2020 by Anthem Press. It gives new locations for various early conflicts. Amongst them are Mount Badon in 493 at Braydon, near Swindon, Wiltshire; those of Arthur in 536-7 in southern Scotland and northern England; Degsastan in 603 near Dawyck, on the River Tweed, Scottish Borders; Maserfelth in 642 at Forden, Powys ; and Brunanburh in 937 on the River Browney near Lanchester, County Durham. This work aims to provide a blueprint for locating a range of battles fought during this early period of British history. He was elected a Fellow of the Royal Historical Society in 1997 and of the Society of Antiquaries of London in 1996.
