Siobhan Dowd was born to Irish parents and brought up in London. She spent much of her youth visiting the family cottage in Aglish, County Waterford and later the family home in Wicklow Town.

She attended a Catholic grammar school in south London and then gained a degree in Classics at Lady Margaret Hall, Oxford University. After a short stint in publishing, she joined the writer's organization PEN, initially as a researcher for its Writers in Prison Committee.

She went on to be Program Director of PEN American Center's Freedom-to-Write Committee in New York City. Her work here included founding and leading the Rushdie Defense Committee USA and traveling to Indonesia and Guatemala to investigate local human rights conditions for writers. During her seven-year spell in New York, Siobhan was named one of the "top 100 Irish-Americans" by Irish-America Magazine and AerLingus, for her global anti-censorship work.

On her return to the UK, Siobhan co-founded English PEN's readers and writers programme, which takes authors into schools in socially deprived areas, as well as prisons, young offender's institutions and community projects.

During 2004, Siobhan served as Deputy Commissioner for Children's Rights in Oxfordshire, working with local government to ensure that statutory services affecting children's lives conform with UN protocols.
Siobhan has an MA with Distinction in Gender and Ethnic Studies at Greenwich University, has authored short stories, columns and articles, and edited two anthologies.

In May 2007, Siobhan was named one of "25 authors of the future" by Waterstones Books as part of the latter's 25th anniversary celebrations.

Siobhan died on 21st August 2007 aged 47. She had been receiving treatment for advanced breast cancer for 3 years, and did not go gentle into that good night.