Father Michael O'Flanagan (Irish: An tAthair Mícheál Ó Flannagáin) (1876 – 7 August 1942) was a Roman Catholic priest, Irish language scholar and Irish republican active in Sinn Féin, of which he was President in 1933–35.
O'Flanagan was born at Kilkeeven, near Castlerea, County Roscommon, the elder son of Edward Flanagan, a smallholding farmer and Mary Crawley. O'Flanagan's parents were bilingual in Irish and English, engaged in Fenian politics, and members of the Land League. Michael went to national school at Cloonboniffe and secondary school as a boarder at Summerhill College in Sligo, growing very tall. He matriculated in St Patrick's College, Maynooth in 1894 and was a brilliant student, winning prizes in theology, scripture, canon law, Irish language, education, and natural science. In later years he filed patents for protective goggles and house insulation products. He was ordained for the Diocese of Elphin on 15 August 1900 and returned to Summerhill College as Professor of Irish until 1904. The position kindled his enthusiasm for the Gaelic revival. His organisation of the Sligo Feis, a nationalist festival, attracted the attention of Sinn Féin.
O'Flanagan supported rural development and Irish self-reliance. He was a skilled orator and started agitating for radical social and political change. In 1904 he was invited to speak on a tour of the United States by his bishop John Joseph Clancy and Horace Plunkett. He was sent to find investment for agricultural and industrial projects in the west of Ireland. In August 1910 he was elected to the executive of the Gaelic League with Fionan MacColuim. His clerical career was hampered by his outspokenness, but through Clancy's political sympathy he was appointed a curate in Roscommon in 1912. The same year, Clancy died and his successor, Bernard Coyne was a conservative who deprecated O'Flanagan's perceived modernism. With his ecclesiastical prospects dim, O'Flanagan began to focus on his political activity.