Ó Neachtain, Seán (c.1640–1729), poet and teacher, was born in the east of Co. Roscommon, son of Tadhg Ó Neachtain, farmer, of Co. Roscommon; nothing is known of his mother. In his early years Seán lived and owned a farm in the parish of Drum in the barony of Athlone, Co. Roscommon, but some time after 1663 he and his three brothers, Fearadhach, Diarmaid and Aodh, suffered forfeiture of lands. It was probably as a result of this that Seán moved east into Leinster, perhaps working as a migrant labourer before eventually making his way to Dublin. He settled in the Thomas St. area of Dublin's Liberties and established himself as a teacher. There is evidence that on at least one occasion this activity brought him to the attention of the law and that he had to leave Dublin temporarily. He was closely involved in the education of his son, Tadhg (qv), and of Tadhg's son, Peadar, and it was undoubtedly this which suggested to Tadhg the idea of casting a series of geographical and historical tracts that he wrote in the form of a conversation between himself and his father, with Seán as teacher providing the information in response to Tadhg's questions.
Though it is not known where Seán Ó Neachtain himself received his education, he was certainly highly literate in Irish and English, and to some extent in Latin also. He was intimately acquainted with a number of priests who ministered in the Liberties area of Dublin and was associated with a group of poets, scholars, and scribes whom his son Tadhg had gathered around himself in Dublin, and who were in frequent contact with both Seán and Tadhg. Of this circle their most regular associates were the scribes Seán Mac Solaidh from Stackallen, Co. Meath, Risteard Tuibear (qv) from Castleknock, Co. Dublin, and Muiris Ó Nuaba, a Munsterman. Together with Tadhg, these three produced a large amount of manuscript material, copying and recopying what they could obtain of manuscripts from earlier times. They performed another function also: Seán Ó Neachtain was a prolific writer, and his emanuenses who made the first fair copies of his work were his son, Tadhg, and Mac Solaidh, Tuibéar, and Ó Nuaba.
A significant portion of Seán Ó Neachtain's writing consists of translations of pious works such as hymns, moral treatises, and saints’ lives. When the originals were in languages other than English (e.g. Latin, Italian) he frequently worked from English versions. He was a prolific composer of prose and verse. Apart from a few exceptions, his personal lyrics lack a sense of true engagement with his subject matter. His most extensive verse works are long narrative poems; in these, though the narrative is clear and well controlled, there is a fatal tendency to dullness. However, this tendency is offset by an element of ribald humour in those of his poems that have a satirical thrust. Some of his verse is of considerable interest to the social and political historian. A man of strong Jacobite sympathies, Ó Neachtain composed a number of poems on political themes. In one he lashed a group of catholic clergy who had taken the 1709 oath of abjuration, rejecting the claim of James III to the crown and asserting Queen Anne's title; another consists of bitter vilification of Queen Anne herself; while a third, written in 1714, attacks King George who in that year had ascended the throne. The correlative of these diatribes is to be found in poems in which he laments the sad fortunes of Ireland and prays for the return to power of the Stuart king. Integral to all this is the religious aspect: he appeals for loyalty to the true, i.e. catholic, religion, and condemns the followers of Luther and Calvin and the members of other sects, quakers and anabaptists.
As a Jacobite Ó Neachtain gave expression in two poems, one in Irish and one in English, and in a prose work in Irish, to the high regard in which he held James Fitzjames (qv), duke of Berwick, who was the illegitimate son of James II (qv). The Irish poem demonstrates clearly Ó Neachtain's skill in handling a number of very different metrical forms, while the prose work, ‘Jacobides agus Carina’, provides evidence of his ability to fictionalise history, since the plot follows closely Berwick's career as a soldier in the war against the Turks in 1687 and in the Spanish war down to 1707, while the hero's involvement with the lady Carina provides a romantic interest. Two other prose works by Ó Neachtain are mock-heroic tales of great length and complexity.
His fourth prose fiction, Stair Éamoinn Uí Chléirigh, is the only one to have appeared in print (ed. Eoghan Ó Neachtain, 1918; ed. William Mahon, 2000), and is without question his most important and most modern work. Though there is a strong element of allegory in the treatment of the material, there is also a vibrant realism in the handling of many aspects of the story, the plot of which charts an alcoholic's battle with the demon of drink, his descent into utter degradation, and his subsequent recovery. Unfortunately the end of the story is unsatisfactory, Ó Neachtain's interest in and concern for his native language frustrating his sense of literary form. On his recovery the hero of the story sets himself up as a schoolteacher and in his school meets a youth who insists on speaking unintelligible English which is a barbaric literal translation of Irish. In an appendix which offers a poignant commentary on the contemporary, ongoing linguistic shift from Irish to English, the sad performance of the first youth is placed in juxtaposition to the richly fluent Irish of another whose command of his native language has been enriched by his exposure to literature in Irish.
Seán Ó Neachtain died on 9 March 1729. He married (a. 1671) Úna Ní Bhroin, who may have been a relation of Edmund Byrne (qv), archbishop of Dublin 1707–24. They lived in the Thomas St. area of Dublin and had three children, Tadhg, Lúcás, and Anna.