He started in theatre, doing voice-over work for commercials. His first big break came in a small but memorable part in the Oscar-winning West Side Story in 1961. A few years later he starred in The Addams Family (1964-1966) as Gomez Addams, the macabre head of the family.
He has continued to work, appearing in a string of "Killer Tomatoes" films as Professor Gangreen. Astin teaches acting and directing in the Writing Seminars Department at his alma mater, Johns Hopkins University. He has five sons, David, Allen, Tom, Sean (adopted) and Mackenzie. Sean and Mackenzie are also successful actors.