He studied Pharmacy in Santiago and practised in Monforte de Lemos and Palas de Rei (Lugo). Since 1940 he has been a pharmacist-inspector and member of the Association of Pharmacists.
Eduardo Seijas published several books such as El Camino Francés en la provincia de Lugo (in collaboration with Amando Losada), Clave de heráldica gallega, Clave de heráldica española, Clave de heráldica jacobea, etc. He directed the hydrologic maps of Lugo, Ourense, A Coruña, Guipúzcoa, Logroño, Ciudad Real and Jaén. He also wrote Pequeña historia de un gran café (unpublished).
Eduardo Seijas was awarded the bronze medal of the General Council of Pharmacist Associations of Spain and the command of the Order of Alfonso X, the Wise and the command with plaque of the Health Civil Order.