Her first published work was a series of saccharine-sweet articles in the Anglo-Celt in January–March 1895, Glimpses of Breffni and Meath, appeared, after which the editor, Edward O'Hanlon encouraged her to study literature.

[citation needed] In February 1887, she signed up to the "Irish Fireside Club", a new column in the Weekly Freeman edited by Rose Kavanagh, symptomatic of the expanding field of children's literature during the fin de siècle.

[citation needed] This club boasted over 60,000 child members during its height, and facilitated the mass-indoctrination of a generation of Irish children into the cultural nationalist movement.

Through this initiative, a core group of middle-class and educated female cultural nationalists emerged in the capital city, including Máire Ní Chinnéide and Mary E.L. Butler, who, like O'Farrelly, would go on to play major roles in the Gaelic League's development through the first two decades of the twentieth century, as literary figures, educationalists and language activists.

[5] She convinced Mary Hayden to apply for the Royal University's Senior Fellowship, in an effort to challenge the view that female scholars were ineligible for such awards.

[7][8][9] During the summer of 1898, when O'Farrelly had then finished her second year of study at St. Mary's College, Eoin MacNeill arranged for her to visit Inis Meáin, the middle of the Aran Islands, to improve her Irish.

For O'Farrelly and indeed her closest friend Douglas Hyde, who also took an active interest, the Celtic Congress held much in common with the Gaelic League with which they had for so long been involved: its raison-d’être was to nurture and promote scholarship and culture (albeit 'Celtic' rather than Irish); the congress was in theory to be held annually (similar to the Oireachtas); and its leading members were now drawn from educationalist and linguistic circles rather than the more exclusive Dublin Castle circle with which it had been associated at the turn of the twentieth century.

[1] Mary Hayden, Osborn Bergin, Eoin Mac Néill and Robin Flower were among those also involved in the Irish wing of the Celtic Congress.

An oil portrait by Seán Keating was presented to her by the Women Graduates' Association on her retirement from UCD in 1947, after which she lived at 38 Brighton Road, Rathgar, where she died on 5 November 1951.

Prose works include The Reign of Humbug (1900), Leabhar an Athar Eoghan (1903), Filidheacht Sheagháin Uí Neachtain (1911), and her novels Grádh agus Crádh (1901), An Cneamhaire (1902) and the travelogue Smaointe ar Árainn (1902).

[20] Out of the Depths (1921) is a collection of political poetry, composed in reaction to the Irish War of Independence, and it displays how O'Farrelly comes to terms with an Ireland far from her ideal.

It portrays the dystopian nature of English power, as O'Farrelly sees it, juxtaposed with the light, spirituality, purity, truth, hope and unity of Ireland, which could enable its future salvation.

Áille an Domhain (1927), produced in a climate of relative stability, reveals a romantic utopianism, and celebrates a return to a harmonious rhythm of life, uninterrupted by the unnatural nature of war.