Collmenter made his major league debut on April 17, 2011, against the San Francisco Giants.
Collmenter entered the game in the 11th inning of a 5–5 game.
He pitched two perfect innings with two strikeouts.
The Diamondbacks would go on to win the game in the bottom of the 12th when Stephen Drew drove in Justin Upton for the game's winning run, cementing Collmenter's first big league win.

Collmenter has caught the eye of some observers due to his unusual over-the-top delivery.
It is thought that the deceptiveness of the delivery has attributed to much of his success thus far.
He is the first pitcher since earned runs were recorded in 1912 to have given up four or fewer total earned runs and 20 or fewer total hits in his first six starts.
Although he does not possess superior velocity to his fastball (average 87 MPH), he relies on throwing a sizable amount of cutters and changeups to keep hitters off-balance.
He also throws a curveball less frequently.

In 2011, Collmenter got his first chance to pitch in the playoffs when he faced the Milwaukee Brewers in Game 3 of the Division Series.
The D-Backs won the game 8–1 and Collmenter got the win.
However, the Brewers would go on to win the best-of-five series, 3–2.
Collmenter began the 2012 season in the rotation, but after going 0-2 with a 9.82 ERA in 4 starts and an average of less than 5 innings per start, Collmenter was demoted to the long relief role on April 30, and Patrick Corbin was called up to take his place in the rotation.
On November 3, 2015, the Diamondbacks exercised Collmenter's 2016 option.

On July 30, 2016, the Diamondbacks designated Collmenter for assignment, and released him on August 7.
On August 10, the Cubs signed Collmenter to a minor league deal.
Collmenter made his major league debut on April 17, 2011, against the San Francisco Giants. Collmenter entered the game in the 11th inning of a 5–5 game. He pitched two perfect innings with two strikeouts. The Diamondbacks would go on to win the game in the bottom of the 12th when Stephen Drew drove in Justin Upton for the game's winning run, cementing Collmenter's first big league win.
Collmenter has caught the eye of some observers due to his unusual over-the-top delivery. It is thought that the deceptiveness of the delivery has attributed to much of his success thus far. He is the first pitcher since earned runs were recorded in 1912 to have given up four or fewer total earned runs and 20 or fewer total hits in his first six starts. Although he does not possess superior velocity to his fastball (average 87 MPH), he relies on throwing a sizable amount of cutters and changeups to keep hitters off-balance. He also throws a curveball less frequently.
In 2011, Collmenter got his first chance to pitch in the playoffs when he faced the Milwaukee Brewers in Game 3 of the Division Series. The D-Backs won the game 8–1 and Collmenter got the win. However, the Brewers would go on to win the best-of-five series, 3–2. Collmenter began the 2012 season in the rotation, but after going 0-2 with a 9.82 ERA in 4 starts and an average of less than 5 innings per start, Collmenter was demoted to the long relief role on April 30, and Patrick Corbin was called up to take his place in the rotation. On November 3, 2015, the Diamondbacks exercised Collmenter's 2016 option.
On July 30, 2016, the Diamondbacks designated Collmenter for assignment, and released him on August 7. On August 10, the Cubs signed Collmenter to a minor league deal.
Josh Collmenter