Ganz grew up in Queens, New York. He dropped out of college and moved to Los Angeles, California to pursue a career writing for sitcoms, starting with The Odd Couple. From there, he moved on to writing for the TV series Happy Days and created two of its spin-off series, Laverne and Shirley and Joanie Loves Chachi.
In 1982, Ganz and Mandel teamed up with Happy Days actors Ron Howard - who wanted to start directing - and Henry Winkler - who wanted to move away from his image as the Fonz - to make their first film, a low-budget comedy called Night Shift, which was also actor Michael Keaton's first film. Ganz's second film outing, Splash, launched the careers of Tom Hanks and Daryl Hannah and earned him an Academy Award nomination for Best Original Screenplay.
Ganz and Mandel went on to write several other films, four more of which were also directed by Howard, and one of which had Penny Marshall, who starred in Laverne and Shirley, as director. Four of their films have featured Billy Crystal, two have featured Tom Hanks, and two are about baseball. Ganz and Mandel are also widely used as Hollywood script doctors, known for their reliability and fast turnaround time.
Ganz lives in Los Angeles with his wife of more than 25 years. They have three children.
Screenwriting credits (in Collaboration with Babaloo Mandel)
- Night Shift (1982)
- Splash (1984) - Oscar nomination for Best Original Screenplay
- Spies Like Us (1985)
- Gung Ho (1986)
- Vibes (1988)
- Parenthood (1989)
- City Slickers (1991)
- Mr. Saturday Night (1992)
- A League of Their Own (1992)
- Greedy (1994)
- City Slickers II: The Legend of Curly's Gold (1994)
- Forget Paris (1995)
- Multiplicity (1996)
- Edtv (1999)
- Where the Heart Is (2000)
- Robots (2005)
- Fever Pitch (2005) (adapted from the Nick Hornby book)
- Tooth Fairy (2010)
Selected television credits
- Hiller and Diller - executive producer
- Joanie Loves Chachi - creator, writer, and producer
- Laverne and Shirley - co-creator, writer, and producer
- Happy Days - writer and supervising producer
- The Odd Couple - writer