The actress is best known for her six-year stint on the comedy sketch show, with memorable characters including 50-year-old Sally O'Malley and Catholic schoolgirl Mary Katherine Gallagher.
More recently, Shannon was seen in HBO's "Enlightened" and ABC's "The Middle," the entertainment industry publication reported Friday.
Shannon published her first children's book, "Tilly the Trickster" in 2011 and in 2012, she voiced a part in the Oscar-nominated animated film, "Hotel Transylvania."
She is next set to appear in the ensemble comedy "Larry Gaye: Renegade Male Flight Attendant," The Hollywood Reporter said.
She is still represented by Framework and attorney Steve Warren of Hansen Jacobsen, and by WME for personal endorsements.
Notable deaths of 2014 [PHOTOS]