Marie Brennan is the pen name of an author born in 1980 in Dallas, Texas, and graduated from Harvard University with a B.A. in archaeology and folklore. She attended Indiana University Bloomington and completed the coursework for a Ph.D. in cultural anthropology and folklore, but left in 2008 to write full-time. Brennan draws heavily on her academic background in her writing, taking inspiration from many real-world cultures and historical periods; she explores various aspects of world history and culture and how those inform her work in her New World Patreon, as well as on her website, Swan Tower: https://www.swantower.com/. She currently lives in northern California.

Her short story "Calling Into Silence" won the Isaac Asimov Award for Undergraduate Excellence in Science Fiction and Fantasy Writing in 2003; "The Legend of Anahata" won an Honorable Mention that same year. Her first publication was "White Shadow" in the anthology Summoned to Destiny, ed. Julie Czerneda, in 2004. In 2006 Warner Books published the fantasy duology of Doppelganger and Warrior and Witch. This was followed by her "Onyx Court" series of historical fantasies - set at various points in the history of London under which resides a court of Fae whose politics intertwine with the world above: Midnight Never Come (2008), In Ashes Lie (2009), A Star Shall Fall (2010) and With Fate Conspire (2011). In 2012, Brennan joined the online Book View Cafe and published on it the Wilders urban fantasy series, consisting of 2 novels and 2 shorter works published between 2012-2021.

Brennan's next fantasy series was set in a pastiche of Regency/Victorian Britain (and parts elsewhere). The titular character of The Memoirs of Lady Trent is a redoubtable lady adventurer and naturalist searching the world for evidence of long-vanished dragons, along the way facing and overcoming ingrained social prejudice against women. Lady Trent's adventures are chronicled in five volumes: A Natural History of Dragons (2013), The Tropic of Serpents (2014), Voyage of the Basilisk (2015), In The Labyrinth of Drakes (2016), and Within The Sanctuary of Wings (2017). A sixth volume, Turning Darkness Into Light, was released in 2019 with a new protagonist following in Lady Trent's footsteps. The series received a 2018 Hugo Award nomination for Best Series.

Brennan's more recent work has gone in several different directions. From 2016-2017, Brennan produced the 'Varekai' series of fantasy novellas, which tell the story of the mysterious warrior Ree and her quest to uncover her origins. In 2020, Brennan pulled together various of her shorter works together with a new framing chapter into the novella Driftwood, taking place in a fantasy world consisting wholly of older worlds that are aging and sinking gradually into oblivion. She has written four novels - The Eternal Knot (2019), The Night Parade of 100 Demons, The Game of 100 Candles (2023), and The Market of 100 Fortunes (2024) - set in Fantasy Flight Games' card game Legend of the Five Rings universe. In 2018, Brennan collaborated with Michael R. Underwood, Cassandra Khaw, and Malka Older on the original audio production Born to the Blade, featured on Serial Box (now Realm) and based in a world rooted in magical swordplay.

Most recently, Brennan and fellow author Alyc Helms have collaborated (under the joint pen name M.A. Carrick) on the Rook and Rose fantasy trilogy; the first volume, The Mask of Mirrors, was released in early 2021. The second volume, The Liar's Knot was released later that year, and the final volume, Labyrinth's Heart, came out in August 2023, with an additional story, "The Naming of Knots", released that same month. Brennan also released a fantasy novel from Titan Books in 2023, The Waking of Angantyr.

Brennan has written numerous works of short fiction, many of which have been assembled in five different collections, available through Book View Cafe. Since her first story in 2002, she has written close to 100 short stories, including, among her most recent, "This Living Hand" (2022), which was nominated for the 2023 WSFA Small Press Award. Most recently, she has been nominated, along with Yoon Ha Lee, for the 2023 Nebula Award for Game Writing for her work on Ninefox Gambit: Machineries of Empire Role Playing Game.