Lily O’Brennan, sister of Áine Ceannt, was born in Dublin in 1878. She was a writer and playwright and joined Cumann na mBan upon its inception; she was a member of the Inghinidhe Branch. During the Rising she served with the Marrowbone Lane garrison. She was arrested and held in Kilmainham Gaol and was released on 8 May, the day of her brother-in-law, Éamonn Ceannt’s execution in the gaol. She continued to be involved in the Republican movement and was a clerk for the National Aid Association which later amalgamated with the Prisoner’s Dependents Fund. She also worked at this time locating the graves of Volunteers killed during the Rising and marking them. A member of Sinn Féin she was co-opted onto its Executive Committee as well as being a member of the Executive of Cumann na mBan.
During the War of Independence she was a District Judge in the Republican Courts while also working for the Department of Labour. With Eilís Ní Riain she was responsible for ensuring the safety of wounded Volunteers and upon receiving word of an impending raid they would have to get the men away to another hospital, this work had to be done late at night. She oversaw the Belfast Boycott in Dublin and at the time of the Treaty negotiations she was Private Secretary to Arthur Griffith. She opposed the Treaty and became Secretary to Erskine Childers.