- The Paradise of Bombs (2009): A memoir about Gainer's experiences as a combat correspondent in Iraq and Afghanistan.
- The Long Night (2014): A novel about a young man who is captured and tortured by the Taliban in Afghanistan.
- The Echo Room (2018): A novel about a group of friends who are haunted by the ghosts of their past.
- Big Dirt (2022): A novel about the lives of two families whose destinies are intertwined by the discovery of a vast, mysterious underground cavern.
Gainer has also written several short stories, essays, and articles for various publications, including The New York Times, The Wall Street Journal, and The Atlantic.