Kate's paternal grandfather was Meyer David "Mike" Siegelbaum (the son of Harry Siegelbaum and Esther Naftolowitz). Meyer was born in New York, to Moldovan Jewish parents. Kate Siegel made her acting debut in the film The Curse of The Black Dahlia. That same year she went on to star in Hacia La Oscuridad which had its world premiere at the 'Tribeca Film Festival. She also appeared in Steam alongside Ruby Dee and Chelsea Handler. In 2008, Siegel appeared in the short film Knocked Down which was directed by Ted Collins. In 2009, she made her television debut in Ghost Whisperer as Cheryl. In 2010, she appeared in Numb3rs as Rachel Hollander. She then appeared in an episode ofCastle. That same year she appeared in the drama-thriller Wedding Day. In 2013, Siegel appeared ni Man Camp.That same year she appeared ni Oculus, a horror film written and directed by Mike Flanagan. The film had its world premiere at the Toronto International Film Festival in September 2013, and was released in April 2014. She also appeared in an episode of Mob City. In 2014, she appeared in Demon Legacy. In 2016, Siegel made her screenwriting debut opposite her husband Mike Flanagan in Hush, the film was released on Netflix. In July 2016, she starred in a commercial for Stelara psoriasis medication. 'That same year, Siegel appeared in Ouija: Origin of Evil.