He studied Latin and Humanities at the Seminary of his city. Then she studied Medicine in Madrid taking his degree in 1877. He was republican and liberal and defended his ideas to death. In 1888 had a civil wedding with Mª del Milagro Antonia Andia Villar. Their two children had already been born before the wedding, which was criticised by the clergy. As he did not consider himself an important person, he rejected his nomination to become a member of the Galician Academy. Some years later he would bestow on the Academy a lot of material about lexicon and folklore he had made.He was buried in a civil cemetery and some conservative newspapers from Lugo such as La Voz de la Verdad and El Norte de Galicia did not publish the news about his death. However, there were thousands of people in his funeral showing affection and respect for him. In October 1921, he was paid a great homage.
He published hardly any book during his life. In 1910, he received a prize in a poetry contest in Vigo with his poem Un galo. His book Cantares Gallegos was published the year before his death. It is a short volume with 244 four-verse poems.In 1910, he published the volume Apuntes para la Geografía médica del distrito municipal de Mondoñedo, which is perhaps the first local monograph about health themes.In 1970, Franco Grande published in Galaxia Leiras' complete work, which consisted of the following productions:a) Cantares Gallegos (244 poems in the volume of 1910).b) 58 unpublished poems.c) Sentences, riddles and proverbs.d) A wide vocabulary.
The Galician Academy dedicated him ?O Día das Letras Galegas? (The Day of the Galcian Letters) in 1983.