Kristen Britain was born in Batavia, New York, and grew up in the Finger Lakes region of the state. She graduated from Ithaca College in 1987 with a degree in film production (and a minor in writing). Following graduation, Britain, inspired by a conversation she had with an National Park Service ranger at Women's Rights National Historical Park in Seneca Falls, NY,  herself became a ranger. Over the years she worked at Clara Barton National Historic Site, Lowell NHP, Acadia NP, Mammoth Cave NP, Rocky Mountain NP, and Women’s Rights NHP.

In 1992 Britain moved to Maine, and the natural setting of Acadia National Park helped inspire and shape her fantasy writing. DAW published her first novel, Green Rider, in 1998 while Britain was still employed with the NPS. The novel tells the story of young Karigan G'ladheon, a merchant's daughter who, while running away from her home, through fate and circumstance becomes a "Green Rider", an elite messenger in the service of the king of Sacordia. The letters she finds herself delivering catapult her into a high-level political and magical conspiracy. Green Riderwas a finalist for the Compton Crook/Stephen Tall Memorial Award for Best First Novel of 1998 and for the 1998 IAFA William L. Crawford Fantasy Award. It also placed #5 in the 1999 _Locus_Poll Awards for Best First Novel.

The sequel to the novel, First Rider's Call, was released in 2003. Karigan's adventures have continued through several additional novels in the series: The High King's Tomb (2007), Blackveil (2011),  Mirror Sight (2014), Firebrand (2017), and the most recent, Winterlight (2021). Blackveil was nominated for the 2012 David Gemmell Award for Best Fantasy Novel. Britain published a prequel novella, relating an early adventure of Green Rider Laren Mapstone, entitled Spirit of the Wood in 2023.

Britain has also written several pieces of short fiction, including "Avalonia" (2001), "Linked, on the Lake of Souls" (2002), and "Chafing the Bogey Man" (2008), among others. Some of her short fiction was published in the 2018 collection The Dream Gatherer.

She currently resides in Maine.