Katie Alender (rhymes with "calendar" but spelled differently) grew up in South Florida. She is the third of four children, with three sisters and one brother. Alender attended high school at the Palm Beach County School of the Arts, where she studied Communication Arts. She later attended the Florida State University Film School, after which she moved to Los Angeles to work in TV production and development.

Alender's love for writing, reading, and sewing (especially quilts) is evident in her life. She enjoys spending time with her husband, daughters, and her dogs, Scooter and Frodo. Her first publication was an article titled "So You Want to Live On Mars?" in Sassy magazine in December 1991.

In 2009, Alender's first book, Bad Girls Don't Die, was published by Hyperion, followed by two sequels, From Bad to Cursed (2011) and As Dead As It Gets (2012). She also published Marie Antoinette, Serial Killer (2013), Famous Last Words (2014), and The Dead Girls of Hysteria Hall (2015) with Scholastic, Inc. In 2020, she published The Companion for Penguin, which won the Edgar Award for Best Young Adult Novel in 2021.

She is a member of SCBWI (Society of Children’s Book Writers and Illustrators), MWA (Mystery Writers of America), and ITW (International Thriller Writers). Despite not liking scary books or movies, her works are often categorized as such. Alender humorously admits to being a huge fan of speaking about herself in the third person.