Born in City Quay, Dublin, she was a midwife at the National Maternity Hospital, Holles Street, and member of Cumann na mBan. O’Farrell acted as a courier both before and during the Rising, and was one of just three women in the GPO under the decision to evacuate the building. She played a key role after the surrender, delivering messages to both Irish Volunteer leaders and the British. Pearse was accompanied by O’Farrell when he surrendered to General Lowe.
Though partly obscured by Pearse, she is seen a photograph taken at the moment of the surrender — but was removed from subsequent versions. O’Farrell died in Fatima House in Bray, Co Wicklow in 1957 and is buried in the Republican Plot at Glasnevin Cemetery alongside Julia Grenan who was with her in the GPO. A Nurse Elizabeth O’Farrell Foundation was set up to support postgraduate studies in the field of nursing.