Walton was born in Aberdare, in the Cynon Valley of Wales. She went to Park School in Aberdare, then Aberdare Girls’ Grammar School. She lived for a year in Cardiff and went to Howell's School Llandaff, then finished her education at Oswestry School in Shropshire, and at the University of Lancaster. She lived in London for two years, lived in Lancaster until 1997, then moved to Swansea, where she lived until moving to Canada in 2002.

Walton has been writing since she was 13, but her first novel was not published until 2000. Before that, she had been published in a number of role-playing game publications, such as Pyramid, mostly in collaboration with her husband at the time, Ken Walton. Jo Walton :: Pen & Paper RPG Database Walton was also active in online science fiction fandom, especially in the Usenet groups rec.arts.sf.written and rec.arts.sf.fandom. Her poem "The Lurkers Support Me in E-Mail" is widely quoted on it and in other online arguments, often without her name attached. IRoSF: Login Required

Her first three novels, The King's Peace (2000), The King's Name (2001), and The Prize in the Game (2002) were all fantasy and set in the same world, which is based on Arthurian Britain and the Táin Bó Cúailnge's Ireland. Her next novel, Tooth and Claw (2003) was intended as a novel Anthony Trollope could have written, but about dragons rather than humans.

Farthing was her first science fiction novel, placing the genre of the "cozy" mystery firmly inside an alternate history in which the United Kingdom made peace with Adolf Hitler before the involvement of the United States in World War II. It was nominated for a Nebula Award, a Quill Award, the John W. Campbell Memorial Award for best science fiction novel, and the Sidewise Award for Alternate History. A sequel, Ha'penny, was published in October 2007 by Tor Books, with the final book in the trilogy, Half a Crown, published in September 2008. Ha'penny won the 2008 Prometheus Award (jointly with Harry Turtledove's novel The Gladiator) and has been nominated for the Lambda Literary Award.

In April 2007, Howard V. Hendrix stated that professional writers should never release their writings online for free, as this made them equivalent to scabs. Walton responded to this by declaring 23 April as International Pixel-Stained Technopeasant Day, a day in which writers who disagreed with Hendrix could release their stories online en masse. In 2008 Walton celebrated this day by posting several chapters of an unfinished sequel to Tooth and Claw, Those Who Favor Fire.

In 2008, Walton began writing a column for Tor.com, mostly retrospective reviews of older books.

Walton moved to Montreal, Quebec, after her first novel was published. She is married to Ireland-born Dr. Emmet A. O'Brien. She has one child, a son named Alexander.

Novels

• The King's Peace (October 2000, Tor Books, ISBN 0-312-87229-1)
• The King's Name (December 2001, Tor Books, ISBN 0-312-87653-X)
• The Prize in the Game (December 2002, Tor Books, ISBN 0-7653-0263-2)
• Tooth and Claw (November 2003, Tor Books, ISBN 0-7653-0264-0)
• Farthing (August 2006, Tor Books, ISBN 0-7653-1421-5)
• Ha'penny (October 2007, Tor Books, ISBN 0-7653-1853-9)
• Half a Crown (August 2008, Tor Books)
• Lifelode (February 2009, NESFA Press, ISBN 1-886778-82-5)
• Among Others (January 2011, Tor Books)

Other works

• GURPS Celtic Myth (with Ken Walton) (1995, roleplaying supplement)
• Muses and Lurkers (2001, poetry chapbook, edited by Eleanor Evans)
• Realms of Sorcery (with Ken Walton) (2002, roleplaying supplement)