Zaun, the nephew of former MLB catcher Rick Dempsey, was a high school teammate of Mark Loretta.

Zaun and Loretta attended Saint Francis High School in La Cañada, California, and graduated in 1989.

[5] After winning a World Series with the Marlins in 1997, he became their starting catcher to finish out the 1998 season when Charles Johnson and then Mike Piazza were traded.

[6] Prior to the 2006 season, the Blue Jays signed Bengie Molina as the everyday catcher, making Zaun the backup.

Zaun hit a game-winning two-run homer off the Tampa Bay Devil Rays' Jason Childers in his return on April 8.

[15] Zaun was claimed off waivers by the Tampa Bay Rays GM Andrew Friedman in exchange for Rhyne Hughes on August 7, 2009.

[21] In January, Zaun signed a minor league deal with the San Diego Padres, with an invitation to spring training.

In the report, Kirk Radomski claimed he sold Deca-Durabolin and Winstrol to Zaun in 2001, after a referral from Jason Grimsley.

Mitchell also explained that former Montreal Expos bullpen catcher Luis Perez claimed to have supplied Zaun with steroids in 2002.

After his retirement, on March 14, 2011, Zaun signed a two-year contract with Rogers Sportsnet to become their studio MLB analyst.

On May 10–11, 2011 Zaun filled in as the color commentator on the NESN broadcast of a Red Sox series against the Blue Jays when the normal broadcaster, Jerry Remy was ill.[28] On November 30, 2017, Rogers Communications announced Zaun's employment had been terminated after an investigation into complaints of improper conduct from several female employees.

[32] On January 2, 2025, Zaun was hired to serve on the coaching staff of the Tigres de Quintana Roo of the Mexican League.