He studied Secondary Education in Ourense and started to show his vocation for writing with a newspaper called El Averno, which he delivered to his partners at school. Some years later, he won a literary prize, being Vicente Risco the president of the panel. In 1960, he moved to Santiago to study Philosophy and Arts, where he met and made friends with Ramón Piñeiro. During the university period, he took an active part in student demonstrations through the Student Democratic Association.
In 1965, he published his first stories in the magazine 'Grial' and his first and successful book, Vento Ferido, in 1967 (a collection of stories). In 1968, he wrote A galiña azul (a book for children) and published his first novel Cambio en tres. He wrote other books for children such as Un polbo xigante, the theatre play As laranxas máis laranxas de tódalas laranxas (with this play he was awarded 'O Facho' Prize) and the story O can Rin e o lobo Crisón, which was translated into Catalan, Basque and Castilian. In 1972, he translated Le petit prince by Saint-Exupéry into Galician (O principiño) and some years later, he translated Tordyveln flyger i skymningen by María Gripe (Os escaravellos voan á tardiña). In 1976, he got the Galician Narrative Prize, awarded by the National Critic Association for his work Xoguetes para un tempo prohibido. With this work, he also got the prize awarded by 'Galaxia' publishing house to celebrate the 25th anniversary of its foundation. In 1977, he entered the Galician Academy with the speech 'A crise do 98 na literatura galega' and two years later, in 1979, he returned to the short story with his book Os escuros soños de Clío. In 1980, he published the novel Ilustrísima (it was also translated into Castilian) and Os mortos daquel verán in 1986 (it was also translated into Castilian). After a long literary silence, he published the novel Deus sentado nun sillón azul (1996). In the last years, Carlos Casares wrote a biography of Fray Martín Sarmiento and wrote O sol de verán, which was left unpublished although it is expected to be published soon.
Carlos Casares took an active part in the elaboration of the Law about Linguistic Normalisation. He was a member of the Galician Academy, 'Penzol' Foundation and 'Otero Pedrayo' Foundation. In 1996, he was elected president of the 'Consello da Cultura Galega' replacing Filgueira Valverde. He directed 'Galaxia' Publishing House and edited the magazine 'Grial'. Carlos Casares was awarded several prizes such as 'Fernández Latorre' Journalism Prize (1983), 'Xunta de Galicia' Prize for all his work (1989) and 'Julio Camba' Journalism Prize (1995). From April 1988 until his death, he collaborated in the newspaper La Voz de Galicia with a daily column titled 'A Marxe'.