Tom was born in Hinsdale, Illinois. Her twin brother, actor David Tom, and older sister (by three years), Heather Tom, have both won Emmys for their performances on CBS's The Young and the Restless (1973).

Tom currently stars in the IFC original The Minor Accomplishments of Jackie Woodman as Tara, an underling at a film production company.

Before her fame on The Nanny, she was known for playing the role of Scott Scanlon's sister Sue on Beverly Hills, 90210 during its earlier years on the air.

Also, in the early 1990s, she played 'Ryce Newton' in the successful family movie Beethoven and the sequel Beethoven's 2nd. She did not appear in Beethoven's 3rd and Beethoven's 4th as she had grown up too much for her specific role, although she did reprise her role as the voice of Ryce in the cartoon spinoff.

From 1998–2006 she provided the voice for Supergirl in the DC Animated Universe. In 2000, she played Sarah Bryan in the Fox Family TV film Ice Angel as well as Tracy in Panic. In 2001, she portrayed a teen reporter named Cassie in The Princess Diaries.

Tom played a small but important role in an episode of Burn Notice that originally aired on September 20, 2007. The episode was titled "Loose Ends," and her character was named Melissa.

She starred in the Lifetime movie Her Only Child, which premiered on March 22, 2008. She guest starred alongside brother David (who played her character's brother) in an episode of Criminal Minds which originally aired on April 2, 2008. She also guest starred on an episode of Cold Case which aired on May 4, 2008.