Grossman's career began in the 1950s on the daytime drama As the World Turns. For extended period of time during his career he was credited as "Robin Thomas". He attended the Carnegie-Mellon University and majored in drama and art. In addition to acting he creates statues. A company named "Tiffany & Co." displayed his sculptures through the years 1977 and 1978 in New York City.
In 1987, he appeared in Summer School and in 2002, The Banger Sisters, starring Goldie Hawn and Susan Sarandon. He began appearing on the CBS procedural drama CIS: Miami, CSI: NY and CIS: Crime Scene Investigation from 2003 through 2007. He has had multiple reoccurring roles on the television series Party of Five, Damages, The Division, Queer as Folk, Matlock and Who's the Boss?.