Born Miriam O’Connor to Michael O’Connor, a bank manager with five children including Valerie, Michael and Fidelma, she goes to school in the Convent of the Sacred Heart in Roscrea, County Tipperary, and in Bregenz, Austria. She goes to college at both the University of London and University College Dublin (UCD). After college she works initially as a speech and language therapist, an occupation which leads to the publication of one of her non-fiction books. She also studies drama in London, at the London Academy of Music and Dramatic Art (LAMDA) under Frieda Hodgson.
Gallagher is commissioned to write essays for The Irish Times, the Irish Medical Times and various journals. She takes up writing screenplays and stage plays. The result is a prolific list of productions which have been staged around the world as well as broadcast by RTÉ and the BBC.
Gallagher varies work from plays to speech therapy, as well as working with prisoners, and this leads her to be a visiting lecturer at universities across the globe. She is deeply involved in the organisations of her craft, leading her to being a member of Irish PEN, both on its committee and as vice president, on the Irish Writers’ Union committee as well as a council member of the Society of Irish Playwrights. Over the years she wins a number of awards including the Arts Council and European Script Fund Awards, the MHA TV Script Award, and the EU Theatre Award.
Gallagher’s husband is Gerhardt Gallagher. They live in Dublin and have three children, Mia, Donnacha, and Etain. In 2012 she is diagnosed with cancer and kidney disease. She dies on January 15, 2018.