John Wasdin, a right-handed pitcher, embarked on his Major League Baseball journey when he was drafted by the Oakland Athletics in the first round of the 1993 MLB Draft. He made his debut with the Athletics on August 24, 1995. During his time with Oakland, Wasdin showed potential as a starting pitcher, but his tenure with the team was relatively short-lived.

In 1997, Wasdin was traded to the Boston Red Sox, where he spent the next few seasons. His role with the Red Sox varied, as he was utilized both as a starter and a reliever. Wasdin's time in Boston was marked by a memorable game on April 27, 1998, when he pitched a complete game shutout against the Kansas City Royals. Despite moments of brilliance, consistency was elusive, and he struggled with maintaining a low earned run average.

The year 2000 saw Wasdin traded to the Colorado Rockies, where he continued to face challenges, particularly with the hitter-friendly conditions at Coors Field. His stint with the Rockies was brief, and he was soon on the move again, this time to the Baltimore Orioles in 2001. With the Orioles, Wasdin primarily served as a reliever, but he was unable to secure a long-term spot on the roster.

Wasdin's journey through the majors continued with the Toronto Blue Jays in 2003, followed by a return to the Red Sox later that year. His second stint with Boston was short, and he found himself with the Texas Rangers in 2004. It was with the Rangers that Wasdin achieved a rare feat on April 7, 2005, when he pitched a perfect game for the Triple-A Oklahoma RedHawks, the first in the franchise's history.

In 2006, Wasdin signed with the Pittsburgh Pirates, where he again served as a reliever. His time with the Pirates was marked by a solid performance, but he was released in 2007. Wasdin's major league career concluded with a brief period with the Washington Nationals, although he did not appear in any games for the team.

Throughout his career, Wasdin played for several teams, often transitioning between starting and relieving roles.