Buckner was originally drafted in the 9th round (248th overall) by the Tampa Bay Devil Rays in the 2003 Major League Baseball Draft out of Young Harris College, but chose not to sign and instead played college baseball at the University of South Carolina. He was drafted again in 2004 by the Kansas City Royals in the second round as the 55th overall pick.

In his fourth season in the Royals organization, Buckner was called up to the big league club on August 24, 2007.

On December 14, 2007, Buckner was traded to the Arizona Diamondbacks for infielder Alberto Callaspo.

On June 1, 2010, Buckner was traded to the Detroit Tigers for Dontrelle Willis and cash considerations. He was released on July 25, 2010.

On December 20, 2010, Buckner was signed by the Colorado Rockies to a minor league deal with an invite to spring training. Buckner had hoped to compete for a spot on the roster, but spent the entire season in Triple-A with the Colorado Springs Sky Sox where he was 4-8 with a 6.03 ERA in 23 appearances. He was traded for a player to be named later however the Rockies never bothered to claim the other player.

On March 2, 2012, Buckner signed a minor league deal with the Boston Red Sox with an invitation to their minor league camp. He was expected to compete for a starting pitching role in their system. Buckner began the season with the Double-A Portland Sea Dogs. He was called up to the Triple-A Pawtucket Red Sox but never reached the major league club. He elected free agency at the end of the season, in which he had a 3.65 ERA in 27 starts.

Buckner signed a minor league deal with the Los Angeles Angels on November 14, 2012. He was assigned to the Triple-A Salt Lake Bees. He was called up to the Angels on May 16 and made his first start since 2010 on May 25, 2013. He was designated for assignment on May 26, 2013. He was designated for assignment again on July 25, 2013. He was designated for assignment a third time on August 23, 2013.

On April 21, 2014, the San Diego Padres signed Buckner to a minor league deal. On May 24, the Padres selected his contract from the Triple-A El Paso Chihuahuas to make a start against the Chicago Cubs that night. He was designated for assignment the next day, and outrighted back to El Paso on May 27.

Buckner signed a minor league deal with the Milwaukee Brewers on August 16, 2014.

On May 9, 2016, Buckner signed a minor league deal with the Arizona Diamondbacks. He became a free agent on November 7, 2016.