Manuel María was the son of two well-to-do farmers, Antonio Fernández Núñez, who was the mayor of Outeiro de Rei, and Pastora Teixeiro Casanova. He went to primary school in his small village of Rábade. In 1942 he moved to Lugo to carry out his secondary studies at the Marist Brothers school. In Lugo, at the age of 20, he began his precocious literary career participating in a conference circuit called "Jóvenes valores lucenses." This helped him get in touch with members of a group that met at the Méndez Núñez cafeteria: Luís Pimentel, Ánxel Fole, Juan Rof Codina, Aquilino Iglesia Alvariño, and others. This was his introduction to Galicianism and the Galician literary world. His friendship with Uxío Novoneyra also dates from this period.
In 1950 he published his first collection of poems, Muiñeiro de brétemas ("Miller of mists"), which inaugurated the so-called "Escola da Tebra" (School of Shadows). His disappointment after failing the entrance exams to the University of Santiago inspired his second collection of poems, Morrendo a cada intre ("Dying every minute"). He did his military service in Santiago de Compostela and there he attended a gathering at Café Español, where he became a great friend of Carlos Maside. He then returned to Lugo, where he studied to become an attorney. In 1954 he won a prize at the Xogos Florais (Floral Games) in Ourense. In 1958 he became a court attorney in Monforte de Lemos, where he remained most of the rest of his life. To that city he dedicated a collection of poems, Cancioneiro de Monforte de Lemos. The following year he married Saleta Goi García in Lugo.
Although poetry was his preferred medium, Manuel María also attempted essays, narratives and plays. He moved away from a pessimistic existentialist position towards social and political commitment. In the troubled period of the 1960s and 1970s, he took part in the undercover reorganisation of the Galician nationalist political parties; he also worked with various organisations devoted to restoring Galician culture, arranging conferences and reciting poems. He managed the Xistral publishing house and together with its founder he ran the bookshop of the same name. He was made a corresponding member of the Royal Galician Academy in 1970, but renounced his membership in a public letter that appeared in the Galician newspapers in 1975.
A grass-root militant of the Galician People's Union and of the Frente Cultural of the Galician National-Popular Assembly, he was elected councillor in Monforte in 1979 for the Galician National-Popular Bloc. He resigned in 1985, and moved to A Coruña to fully devote himself to literary and cultural activities. His column, Walking on Earth, appeared in the newspaper Our Earth. One of the last campaigns in which he took part was in response to the Prestige oil spill disaster, under the names of Burla Negra (" Black Mockery") and the Plataforma Nunca Máis ("Never More" Platform).
In 1997 he was appointed partner of honour of the Galician Writers Association. He was re-admitted to the Royal Galician Academy in February 2003, under the sponsorship of Xosé Luís Méndez Ferrín and others. respondido por Méndez Ferrín.
He died at A Coruña on 8 September 2004, and was buried in the church of Santa Isabel, Outeiro de Rei.