[3] Seosamh was born to Feidhlimidh Mac Grianna and Máire Eibhlín Néillín Ní Dhomhnaill, the daughter of the famous storyteller Johnny Shéamaisín Ó Domhnaill.

[3] He began a teaching career upon his release, but found it difficult to find a permanent position, partly because of his reputation as a former Anti-Treaty IRA member and internee.

[3] Mac Grianna started writing in the early 1920s, and his creative period lasted some fifteen years.

He wrote essays, short stories, travel and historical works, a famous autobiography, Mo Bhealach Féin, and a novel, as well as translating many books.

He was imbued with a strong, oral traditional culture from his childhood, and this permeated his writings, particularly in the early years.

Towards the end of his career, Mac Grianna grew increasingly analytical and critical as he examined the changing face of the Gaeltachtaí and the emergence of an Anglicised Irish Free State with no loyalty to, or sympathy with, a heroic and cultured past.

[3] He was probably the greatest Gaeltacht writer of his time, whose work had developed considerably before he was stricken by a severe depressive psychosis in 1935.