Seosamh Mac Grianna was born in Rannafast, Co. Donegal in 1901.
His brother Séamus Ó Grianna was also a notable writer. Like his brother who was also a teacher, he was interned during the Civil War as a Republican. At least in part due to his disillusion with the new Ireland, he spent the last 30 years of his life in Saint Connall’s, the mental hospital in Letterkenny, Co Donegal.
His works include Dochartach Dhuiblionna agus Scéalta Eile (Baile Átha Cliath, Cú Uladh, 1925); Filí gan Iomrá (Baile Átha Cliath, Oifig an tSoláthair, 1926); An Grá agus an Ghruaim (Oifig an tSoláthair, 1929); Eoghan Ruadh Ó Néill (Oifig an tSoláthair,1931); An Bhreatain Bheag (Oifig an tSoláthair, 1933); Pádraic Ó Conaire agus Aistí Eile (Oifig an tSoláthair, 1936); Na Lochlannaigh (Oifig an tSoláthair, 1938); Mo Bhealach Féin (Oifig an tSoláthair, 1940); Dá mBíodh Ruball ar an Éan (Oifig an tSoláthair, 1940); An Druma Mór (Oifig an tSoláthair, 1969); and Filí agus Felons ([Nollaig Mac Congáil, eagathóir] Baile Átha Cliath, 1987).
A documentary on his life, Dá mBíodh Ruball ar an Éan, was made by BBC Northern Ireland in 1991.
He died in 1990.
the entry for Seosamh Mac Grianna at Search’s Web Guide
Nollaig Mac Congáil, Feasta 5