Together with her husband, Nancy O'Rahilly returned to Ireland to live near sisters Nell and Anna Humphreys.

O'Rahilly contributed to Irish Freedom, editor of An Claidheamh Soluis, the Gaelic League paper.

[3] Nancy O'Rahilly joined Cumann na mBan in 1914 and was elected to its founding Executive Committee.

Her husband Michael Joseph O'Rahilly, was killed during the Easter Rising, having written a note of dying declaration to her.

Her house at 40 Herbert Park, Ballsbridge, County Dublin where she lived with her young family was raided by British soldiers in mid-1916.

[12] She became a Vice-President of Cumann na mBan,[11]: 288  but resigned in 1922, during the Irish Civil War, when her son was fighting for the anti-treaty IRA, which she also supported.