Born to Feidhlimidh Mac Grianna and Máire Eibhlín Néillín Ní Dhomhnaill into a family of poets and storytellers in Ranafast, County Donegal, he attended local primary school until the age of 14.
He trained formally as a teacher in St. Patrick's College, Dublin, 1912–14, and taught mostly in County Donegal until 1920.
[citation needed] He became involved with political matters and was interned as a republican during the Irish Civil War.
[3] His prolific literary output, spanning more than fifty years and including novels, short stories, essays, autobiography, and his famous Rann na Feirste, is a romantic and nostalgic celebration of his native place, its rich oral tradition, poetic speech, colourful characters, local lore, and varied landscape.
[citation needed] Séamus Ó Grianna's novel Caisleáin Óir was developed into a musical and was premiered in An Grianán Theatre, Letterkenny, County Donegal in 2001.