Miami Marlins Minor leagues Koehler signed with the Marlins on June 5, 2008. He was assigned to the
Class-A Short-Season|Low-A Jamestown Jammers of the
New York–Penn League to start his professional career. He went 5–5 for the season with a 3.68 ERA and 58 strikeouts in 15 games. During the 2009 season, Koehler played with the
Single-A Greensboro Grasshoppers, and the
High-A Jupiter Hammerheads. During the 2010 season, Koehler went 16–2 with a 2.61 ERA and 145 strikeouts in 28 starts. At the end of the season, Koehler won the
Southern League Most Outstanding Pitcher Award. He also tied a Jacksonville Suns franchise record with 16 wins. In 2011, he pitched for the
New Orleans Zephyrs of the Triple-A
Pacific Coast League and was 12–7 with a 4.97 ERA. He finished the season with a 5.40 ERA and 13 strikeouts in 13 innings pitched. Koehler began the 2013 season with the Zephyrs and became the franchise's all-time strikeout leader on April 14 when he picked up his 267th against the
Round Rock Express. He was called back up to the Marlins on April 19 to fill a long relief role and made six relief appearances before moving to the rotation to replace
Wade LeBlanc. He earned his first major league
win against the
San Francisco Giants on June 20, pitching seven innings and allowing only one run. He finished the season with a 5–10 record and a 4.41 ERA in 143 innings pitched. He made his first start for the Blue Jays on August 24, pitching five innings, allowing one run, and striking out seven batters in a 2–0 loss to the
Tampa Bay Rays. He was then moved to the bullpen, where he made 14 appearances. Koehler finished the 2017 season with a 2.65 ERA and 18 strikeouts in the 17 innings he pitched for Toronto.
Los Angeles Dodgers On December 20, 2017, Koehler signed a one-year, $2 million, incentive laden contract with the
Los Angeles Dodgers. However, he suffered a strained right shoulder in a spring training game and was shut down for the start of the season. He underwent season ending shoulder surgery in July and was shut down for the season without appearing in any games for the Dodgers. The Dodgers released him on November 20, 2018.
Pittsburgh Pirates On February 6, 2019, Koehler agreed to a minor league contract with the
Pittsburgh Pirates. He was invited to Spring Training for the 2020 season. On March 2, 2020, Koehler announced his retirement from professional baseball. ==Pitching style==