TVGuide.com said the "Firefly" and "Alias" veteran will start playing the recurring character of Gabriela Abrams -- home-schooled Vanessa's warm, opinionated mother -- on the show this fall.
Jessica Szohr plays Vanessa.
"Gossip Girl" is set to begin its third season on the CW Sept. 14.
Notable deaths of 2014 [PHOTOS]
Reports: Mila Kunis gives birth to baby girl