Helen Moloney was born in Henry Street, Tipperary on 2 January 1926, one of a pair of twins with her sister Mary. Her parents were James (1896–1981) and Kathleen Barry Moloney. She had two younger sisters other than her twin, and a brother. Her younger sister Katherine (1928–1989) went on to marry Patrick Kavanagh after a long relationship. Both sides of Moloney's family were involved in the Irish republican movements. Her paternal grandfather, Patrick James Moloney (1869–1947), was a pharmaceutical chemist and Sinn Féin TD in Tipperary from 1919 to 1923, being re-elected in June 1922 as an anti-treaty candidate. Her father was an officer in the 2nd Southern Division and the 3rd Tipperary Brigade during the war of independence, serving with the anti-treaty IRA as director of communications. Her uncle, Con Moloney (1897/8–1951), was adjutant of the 2nd Southern Division serving under Ernie O'Malley and Liam Lynch. Moloney's mother was the older sister of Kevin Barry and was active in Cumann na mBan, the Gaelic League, and Sinn Féin. She worked in the Dáil Éireann department of home affairs, and served as a judge of the republican courts. She toured America and Australia in the early 1920s raising money for the Irish republican cause and was the general secretary of the Irish Republican Prisoners' Dependants' Fund. Moloney's father was a chemist, and struggled to find work until he took a post with the Irish Sugar company in Carlow in 1934.