Typically she writes about damaged or eccentric people in mundane situations, and has a fondness for bleak, isolated settings. Wide Open and Behindlings are set respectively on the Isle of Sheppey and Canvey Island. Her 2004 novel, Clear, is set in London during David Blaine's Above the Below 44 day fast in London in 2003.
Barker's novel Darkmans won the 2008 Hawthornden Prize. Patrick Ness' Guardian review described the book as "phenomenally good" despite it being a "838-page epic with little describable plot, taking place over just a few days and set in...Ashford"