Eileen Delaney was born in Dublin in 1923. She was educated at St. Kevin's School, the National College of Art, Grafton Academy of Dress Designing and the Abbey Theatre School of Acting. She first became involved in politics in 1955 when she was first elected to Dublin City Council. In 1976 she contested the by-election in Dublin South West, following the death of her 47-year-old husband, Noel Lemass, Jnr, a son of former Taoiseach Sean Lemass and a brother-in-law to another former Taoiseach Charles Haughey.
She was elected to Dáil Éireann at the 1977 general election. Lemass was re-elected in the 1981 election, but lost her Dáil seat in February 1982. However she regained her seat in that year's second general election in November 1982. Two years later in 1984 she was elected to the European Parliament. She retired from domestic politics at the 1987 election and from European politics in 1989 when she lost her European seat.