Marie Brennan is the pseudonym of Bryn Neuenschwander, an American fantasy author. Her works include the Doppelganger duology (Doppelganger and its sequel Warrior and Witch); the Onyx Court series; the Memoirs of Lady Trent series; and numerous short stories.

The first of the Onyx Court novels, Midnight Never Come, was published on May 1, 2008, in the United Kingdom, and June 1, 2008, in the United States, and received a four-star review from SFX. The Lady Trent series was a finalist for the Hugo Award for Best Series in 2018.

As an undergraduate at Harvard University, Neuenschwander served as co-chair of the Harvard–Radcliffe Science Fiction Association. After graduating from Harvard, she pursued graduate studies at Indiana University Bloomington, studying folklore and anthropology; in 2008, she left graduate school without completing her PhD to pursue writing full-time.