In 1990, Ziering was chosen as Steve Sanders on the hit series Beverly Hills, 90210. Sanders was a high school student and friend of Brandon Walsh - one of the series' central characters. He is one of only four series regulars to appear on the show for its entire duration. In 1998, Ziering was cast as the voice Dr. Niko "Nick" Tatopoulos in Godzilla: The Series, which was a direct follow-up to the 1998 Hollywood Godzilla re-imagining.
In 2006, Ziering produced, directed and starred in the short film Man vs. Monday, which won the Audience Choice Award at the 2006 Ft. Lauderdale Film Festival. Also in 2006, Ian won the Best Actor Award at the 2006 Monaco Film Festival for his portrayal of Francis in the independent film Stripped Down. Ian has also appeared in the television series JAG, What I Like About You, The Doctors as Erich Aldrich and Guiding Light as Cameron Stewart. He also had a role in the videogame Freelancer as the protagonist, Edison Trent. Ziering replaced Matthew Broderick, who played Nick Tatopolous in the movie. He was a celebrity dancer on Season 4 of Dancing with the Stars; his professional dance partner was Cheryl Burke.
On June 18, 2007, Variety reported that Ziering had auditioned the previous week for the opportunity to succeed Bob Barker as host of The Price Is Right. The job ultimately went to Drew Carey. In May, 2013, it was announced that Ziering would be performing with Chippendales as a celebrity guest star for four weeks at the Rio All Suite Hotel and Casino in Las Vegas. In 2015, he appeared on Celebrity Apprentice on NBC.