He started his education with his father Francisco and finished his career with Fernando de Casas. He was friend of Lucas Ferro Caaveiro. Owing to the great number of works that were carried out in the cathedral, Fernández Sarela was nominated as master builder in 1745 and collaborated with Ferro Caaveiro in the works of the Azabachería façade.
The works on the vaults at San Miguel do Agros Church were carried out in 1745, in Santiago, the Casa del Deán was finished in 1754 and Casa del Cabildo in 1759. Fernández Sarela also worked on the works of the porter's lodge in the old Convent of Conxo.Besides, he worked in the reconstruction of Santo Cristo de Conxo Chapel (1730-1737).Although there are no documents about it, Fernández Sarela is thought to have built and designed other houses situated in different areas of Santiago.