J. Smith-Cameron was born Jeanie Smith. She played violin in school, and was cast in The Diary of Anne Frank as Anne. That's when her acting career took off. She studied theatre in Florida State University, which caused her to be cast in the film Gal Young'Un as the Gal herself. During that time she was called J. Smith, but since this is almost as original as John Doe, she added her grandmother's Cameron to the name, and ever since then, she's been J. Smith-Cameron (with a hyphen). In 2001 she married playwright/screenwriter/director Kenneth Lonergan. They reside in New York City and have a daughter named Nellie Sharpe Lonergan.