After spending the 2001 season in the minors, the Brewers traded him to the San Diego Padres on March 24, 2002, in exchange for Dusty Wathan. He appeared in only 7 games for the Padres and spent most of the season in AAA with the Portland Beavers.
He received a September call-up with the Blue Jays and on September 3, 2006, Barker recorded his first hit as a Blue Jay, a home run off Boston Red Sox starting pitcher Josh Beckett. After the 2007 season, Barker signed a minor league contract with the Cincinnati Reds and played for the Triple-A Louisville Bats the entire year. In 2009, he appeared in 29 games for the Reds, batting .281.
He spent the 2010 and 2011 seasons in the Mexican League.
On September 19, 2025, Kevin was inducted into the Virginia Tech Hall of Fame as part of the Class of 2025.