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She was born in the Curragh army camp, Kildare, Ireland. Her father[who?] had been active in the Irish War of Independence alongside Michael Collins, but favoured the Anglo-Irish Treaty and then joined the National Army.
She grew up in Hatch Street, Dublin, attending Loreto College on St Stephen's Green and then University College, Dublin, graduating in history. The economic historian George O'Brien  supervised her MPhil in economic history looking into Irish emigration to England. She went on to teach economic history in UCD for some years before moving to Southampton University with her husband, Joseph Lee. Two years after her first husband died, she remarried, to James Daly, returning to Ireland with him in 1968. They both were appointed lecturers in Queen's University, Belfast.
She soon became an activist in the civil rights movement, particularly following the introduction of internment without trial by the Stormont government. She was active in the Northern Ireland Civil Rights Association and the Northern Resistance Movement.
She was a militant member of the Prisoners' Relatives Action Committee, and the national Hunger Strike Committee. In that campaign, she worked with Seamus Costello, and soon joined him in the Irish Republican Socialist Party and the Irish National Liberation Army. After Costello was assassinated, she became chairperson, leading the party for two years. During this time she and her husband James were instrumental in opposing Sinn Féin's drift towards federalism.
On 26 June 1980 Miriam Daly was shot dead at home in the Andersonstown area of west Belfast. At the time of her assassination, she was in charge of the IRSP prisoners' welfare. It is believed that loyalists were responsible. She was buried in Swords, County Dublin.
- Straight from the Heart - an interview with Miriam Daly's widower, Jim Daly accessed 24 April 2008
- IRSP: Miriam Daly Commemoration Speech 25 June 2005 accessed 24 April 2008
- Unveiling of Daly/McNamee Plaque 22 June 2003 accessed 24 April 2008