Outman pitched for Forest Park Community College in Saint Louis, before transferring to the Central Missouri State. While playing for the Mules he posted a 10-2 record and helped the Mules finish third in the NCAA Division II World Series. Outman was one of five Mules drafted in the 2005 MLB Draft.
Outman was a prospect in the Philadelphia Phillies organization, and was named the 12th-best prospect in the Phillies organization in 2007.
On July 17, 2008, Outman was traded, along with fellow prospects Adrian Cardenas and Matthew Spencer, to the Oakland Athletics for starting pitcher Joe Blanton.
Outman was called up to the majors for the first time on September 2, 2008, and pitched two scoreless innings that night against the Kansas City Royals, striking out two. Outman's performance in the 2009 season gave him the fan nickname "Out-Man", because of his ability to get the easy outs. Outman's brother, Zachary, was selected by the Toronto Blue Jays, in the 28th round of the 2009 Major League Baseball Draft, out of Saint Louis University.
After a successful first half of the 2009 season starting 12 games for the Athletics. Outman was placed on the disabled list with an injury to his pitching elbow. Outman underwent Tommy John surgery, ending his season on June 30.
Outman, recovering from surgery, missed the entire 2010 season.
In 2011, Outman pitched 58.1 innings (starting 9 games), with a 3–5 record, 35 strikeouts and 3.70 ERA.
On January 16, 2012, Outman, along with pitcher Guillermo Moscoso, was traded to the Colorado Rockies for outfielder Seth Smith.
Outman was traded to the Cleveland Indians on December 18, 2013 in exchange for outfielder Drew Stubbs.
On January 14, 2014, Outman avoided arbitration after filing for arbitration earlier that morning. He was the first player to avoid arbitration in 2014. Cots Contracts reported that he had signed a 1 year/$1.25M contract.
On June 18, 2014, the Indians designated Outman for assignment.
Josh Outman was acquired by the New York Yankees on August 28, 2014 in exchange for a player to be named later or cash considerations. He was designated for assignment on September 22. Outman elected free agency in October 2014.
Outman signed a one-year contract with the Atlanta Braves for the 2015 season. He was released on August 4.
On April 7, 2016, Outman signed with the New Britain Bees of the Atlantic League of Professional Baseball. He was released by the Pittsburgh Pirates on August 13, 2016.
On January 7, 2017, Outman signed a minor league contract with the Washington Nationals. He was released on May 2, 2017.
On May 28, 2017, Outman signed with the Acereros de Monclova of the Mexican Baseball League. He was traded to the Pericos de Puebla on June 24, 2017.
Outman throws five pitches, relying most heavily on a four-seam fastball at 93–96 mph. He also throws a two-seamer (90–95), a slider (80–83), a changeup (78–83), and a curveball (low-to-mid 70s). His changeup is not thrown to left-handed hitters, but is a common pitch against right-handers. He uses his slider a great deal against lefties, but typically uses it against righties only in 2-strike counts. Throughout his career, the slider has been his best swing-and-miss pitch, with a whiff rate of 46% through June 2012.