Born in Chicago, Illinois, Tennant was raised in Flossmoor, Illinois, a suburb of Chicago. His father was Don Tennant, a legendary creative advertising talent with Leo Burnett Agency in Chicago. As a boy, he spent his summers on Old Mission Peninsula in northern Michigan and at Camp Minocqua in northern Wisconsin. He graduated from Homewood-Flossmoor High School in 1973. He studied theater under John Houseman at University of Southern California.
Tennant's first acting role in a motion picture was in 1980 as a college student, Melio, on an all-night scavenger hunt in a surreal film, Midnight Madness which cameo'd cowboy-hatted Pee Wee Herman as a pin ball arcade manager; Andy's first big break in films came when he was cast as a Dancer and chorus member in the movies Grease and Grease 2.
