After graduating from Cardinal Newman High School in Santa Rosa, California in 1993, Dillon entered college at Santa Rosa Junior College and then Texas Tech University. Dillon's career at Texas Tech included a 33 home run season in 1997, a record which still stands today.
On June 3, 1997, he was drafted by the Kansas City Royals in the 7th round of the 1997 Major League Baseball Draft. He played the 1997 season with the Low-A Spokane Indians, the 1998 season with the Single-A Lansing Lugnuts, and the 1999 season with the High-A Wilmington Blue Rocks. He split the 2000 season with the Double-A Wichita Wranglers and the Triple-A Omaha Royals. During his time with Omaha, he suffered a herniated disc in his back. He was sent down to Omaha for the 2001 season.
Following the 2001 season, on December 31, Dillon was drafted by the Minnesota Twins in the 2001 Rule 5 Draft. He was assigned to the Double-A New Britain Rock Cats, where he spent nearly the entire season before being promoted to the Triple-A Edmonton Trappers.
Continued problems with his back, including increasing stiffness, prompted him to retire during spring training 2003. On March 24, 2003, he was released from the Twins. During the year, he underwent back surgery to repair the herniated disc. Following that, he returned to his alma mater, Texas Tech University, to coach its 2003 baseball team. His back felt better, and he decided to return to playing professional baseball.
On March 17, 2004, Dillon was signed as a free agent by the Florida Marlins. He began the 2004 season with the Double-A Carolina Mudcats, before being promoted to the Triple-A Albuquerque Isotopes. He started the 2005 season with Florida, before returning to Albuquerque, only later to be recalled by the Marlins on the same day he made his Major League debut on May 18, 2005; due to a lucky coincidence Marlins starting third-baseman Mike Lowell left the game when a foul pop-up hit by Milton Bradley of the Los Angeles Dodgers hit him in the face when he lost it in the sun; in four at bats, he had one hit and one strikeout. Over the rest of the season, in 36 at bats with the team, he achieved a batting average of .167 and one home run. After the season, he was granted free agency.
Dillon joined the Mazatlán Deer of the Pacific Mexican Winter League late in the 2004-2005 season, helping the team win the championship.
Dillon was signed by the Yomiuri Giants of Nippon Professional Baseball for the 2006 season. He spent the entire season in Japan.
Upon returning to American professional baseball, he signed a minor league contract with the Florida Marlins on December 20, 2006. The following spring, he asked for, and received, his release from the contract.
He then signed a minor league contract with the Milwaukee Brewers on April 1, 2007, and was assigned to the Triple-A Nashville Sounds of the Pacific Coast League. On August 1, 2007, he was called up to the Brewers along with Elmer Dessens when pitcher Scott Linebrink left on bereavement leave and second baseman Rickie Weeks was sent down to Nashville.
Dillon was called up by the Brewers from Triple-A Nashville on May 1, 2008. In a corresponding move, the Brewers designated relief pitcher Derrick Turnbow for assignment.
Following the 2008 season, Dillon was claimed off waivers by the Oakland Athletics.
On January 7, 2009, Dillon was designated for assignment to clear a roster spot for Jason Giambi and was sent outright to the minors.
On May 10, 2009, Dillon was acquired by the Tampa Bay Rays for Adam Kennedy.
On December 18, 2009, Dillon re-signed a minor league contract with the Tampa Bay Rays. Dillon is attempting to add catcher to his list of positions in spring training for the 2010 season.
On MLB.com, he is listed as a retired player.
On December 20, 2013, Dillon was announced as the hitting coach for the National's AAA affiliate Syracuse Chiefs.