He made his professional debut with the Single-A Lake County Captains, where he pitched to a 3.90 ERA and 4-6 record in 26 games.

The next year, Herrmann split the season between the Triple-A Buffalo Bisons, the Double-A Akron Aeros and Kinston, accumulating an 11-8 record and 4.14 ERA between the three teams.

With the Aeros in 2008, Herrmann made 23 starts and, with his 11–6 regular season record and helped lead the team to the 2008 Eastern League championship series.

In 2009, he split the season between the Triple-A Columbus Clippers and Akron, posting a 4-4 record and 2.95 ERA in 49 games.

[1] In a game against the Chicago White Sox, he pitched 1.1 innings and gave up no hits, runs, or walks.

He was credited with his first career hold, retiring all four batters he faced: Gordon Beckham, Juan Pierre, Omar Vizquel, and Alex Ríos.

On March 13, 2013, Herrmann underwent Tommy John surgery, causing him to miss the entire 2013 season.

[14] On November 18, 2015, Herrmann signed a minor league deal with the Philadelphia Phillies that included an invitation to Spring Training.

[15] He was assigned to the Triple-A Lehigh Valley IronPigs to begin the year, where he pitched to a 6-1 record and 1.72 ERA in 27 games.

On November 29, 2016, Herrmann signed with the Tohoku Rakuten Golden Eagles of Nippon Professional Baseball.

On February 18, 2022, Herrmann joined the Toronto Blue Jays' front office in a scouting, player development, and baseball operations role.