When he tried out, he won the role of Young Charlie, with Judd Hirsch, Tony Shalhoub and Jason Biggs, who was also making his Broadway debut.Soon after his run on Broadway, Krumholtz co-starred in two feature films, Life With Mikey (1993) with Michael J.
In September 2005, he was seen in Joss Whedon's science fiction film Serenity as "Mr. Most recently, in early 2006, Krumholtz's 2003 film Kill the Poor screened in New York City at IFC Center and across the country on Comcast's On Demand cable service.
He played Charlie Eppes, a mathematical genius who helped his brother Don (Rob Morrow), an FBI agent, solve crimes using mathematics, on CBS' show Numbers.
The cast of Numbers also included Judd Hirsch and Peter Mac Nicol, who appeared with him in Addams Family Values as a camp counselor.
In 1994, Krumholtz co-starred in his first television series, Monty, with Henry Winkler; the show lasted only a few episodes.
Krumholtz later starred in several short-lived series over the years.