Big was born Jennifer Chan on September 16, 1958, in Harbor City, California. The daughter of Harry, a Chinese stockbroker, and Patrica, a schoolteacher, Jennifer's parents got divorced when she was 6. Patrica Tilly remarried and took Jennifer, her 3 siblings, and her 3 stepsiblings to British Columbia, Canada. Having to relocate constantly with her family, Jennifer had to adjust to each new school, and was a pretty quiet student. At 17, she started out yet again at a new school, this time at St. Stephen's College in Missouri, to study theater. In order to help pay for her tuition, she contributed articles to magazines and earned money by winning 'honorable mentions' in writing competitions. She then headed to college in Los Angeles rather than New York, unlike her sister Meg who starred in Body Snatchers. She made the television rounds, starting with a role as an extra on "Days of Our Lives", then a recurring role as a Mafia moll who snares a straight-laced cop on "Hill Street Blues" in 1984. Also that year she was cast as Shannon Winters on the short-lived sitcom, "Shaping Up", and followed it up with guest appearances on "Remington Steele", "Cheers", and another recurring role on "It's Gary Shandling's Show".
Jennifer was also busy appearing in small parts, in films such as Moving Violations (1985), (her first film when she was 27) He's My Girl (1987), and Rented Lips (1988), one year after the other. In 1988, Jennifer appeared in Johnny Be Good (1988) and High Spirits (1988). After roles in Let It Ride (1989) and Far from Home (1989), Jennifer was finally recognized for her role as auditioning singer Blanche "Monica" Moran in 1989's Fabulous Baker Boys, The (1989). Then more parts came her way, such as in Doors, The (1991), Scorchers (1991) and Made in America (1993), but she finally got her big break when she was cast as Olive Neal, the wife of a mobster, in Woody Allen's Bullets Over Broadway (1994), in 1994. She was nominated for a Best Supporting Actress Oscar, in her convincing portrayal of an untalented, aspiring actress. She has since starred in many hit films such as Liar Liar (1997) with Jim Carrey, Stuart Little (1999) with Michael J. Fox as a stripper in Dancing at the Blue Iguana (2000), and in the hit blockbuster Monsters, Inc. (2001). She has also appeared in theater productions, including "One Shoe Off" -which earned her a Theater World Award in 1993. She is the sister of actress Meg Tilly.