O'Faolain was an active member of Cumann na mBan during the Irish Civil War, acting as a courier, distributing an underground anti-treaty news sheet.
She became disillusioned, believing that many of her fellow republicans were driven by "love for [their] own ruthless selves", which strained relations with Seán but he eventually came to the same conclusion.
They married on 3 June 1928 in Boston's Cathedral of the Holy Cross, spending their honeymoon camping across the United States for two months.
[1] She suffered from near-chronic illness from the 1940s, with some of her ailments being psychosomatic or "stress-maladies" as her daughter characterised them, brought on by her husband's serial infidelities.
O'Faolain was admitted to St Vincent's Hospital, Dublin with recurring internal bleeding, where she died of a stroke on 20 September 1988.
She left her body to Trinity College Dublin for medical research, with her ashes scattered at the lake of Gougane Barra, west Cork.