He studied Secondary Education in Pontevedra and took a degree in Law in Santiago. He also took his doctor's degree in Arts, History section. He worked as a teacher at the Secondary School in Pontevedra. In 1923, he directed the Literature sectioin at the Seminary of Galician Studies. He collaborated in several means of communication and in 1932, he became a member of the Spanish Academy of History. He also became a member of the Galician Academy, the Institute of Galician Studies 'Padre Sarmiento' and many other foundations and academies. He received many prizes and medals.
Filgueira's knowledge ranged over several fields. He wrote more than 300 books and thousands of articles, made speeches and gave lectures. As an example of his wonderful work we can mention the books Guía de Compostela, Castelao escenógrafo, Da épica na Galicia medieval, Don Quijote y el amor trovadoresco, La toponimia gallega, Rosalía no seu fogar and so forth.