Jeannine Hall Gailey was born on April 30, 1973, at the Yale University Hospital in New Haven, Connecticut. She spent her childhood in Los Angeles and Oak Ridge, and her teenage and early college years in Cincinnati, before moving to Virginia, Seattle, and California. Her first degree was a B.S. in pre-med Biology; her second was an M.A. in English, both from the University of Cincinnati. She learned to program a simple computer game when she was seven years old on her father's TRS-80; this probably led to her early career, for a dozen years, as a technical writer, and then a manager of technical writers, for such companies as AT&T and Microsoft. She then returned to college to get her M.F.A at Pacific University in Oregon, and she published her first book of poetry, Becoming the Villainess, at the age of 32.

Gailey works as a poetry book reviewer and has volunteered at many Seattle-area magazines, including Seattle Review, Raven Chronicles, and Crab Creek Review. In 2012-2013, she served as the second Poet Laureate for Redmond, Washington, where her motto was "geeks for poetry, poetry for geeks." In addition to her many works published in poetry journals and elsewhere, she is the author of five books of poetry: Becoming the Villainess, She Returns to the Floating World, Unexplained Fevers, The Robot Scientist's Daughter (2015), and Field Guide to the End of the World (2016). This last work won the 2015 Moon City Press Book Prize for Poetry and the 2017 Elgin Award from the Science Fiction Poetry Association. Her latest book of poetry, Flare, Corona, was published in April 2023 by BOA Editions as #201 in the "American Poets Continuum Series".

She has won a number of awards for her work, including a 2011 Florida Publishers Association Prize for Poetry (for _She Returns to the Floating World),_which was also a finalist for the 2012 Eric Hoffer Montaigne Medal. She was awarded the Dorothy Sargent Rosenberg Poetry Prize in 2007 and again in 2011. Gailey also won "Honorable Mention" in the 2008 Mainichi Haiku Contest. Several of Gailey's poems have been included in major genre anthologies, which include _The Year's Best Fantasy and Horror 2007_and The Year's Best Horror, Volume Six(2014).

Gailey counts among the most influential works on her writing Grimm's Fairy Tales, the Bible, and the works of Margaret Atwood, Kelly Link, AS Byatt, and Haruki Murakami; as well as comic books from the mid-eighties, and Hayao Miyazaki's anime classics. She currently resides in Redmond, Washington, with her husband, cats, and a teeming collection of out-of-print Andrew Lang fairy books, comics, and poetry books.