He made seven starts and six relief appearances, accruing an ERA of 4.06 while striking out 32 batters and allowing 12 walks and 62 hits over 51 innings.

Most of Stammen's 2007 season was spent at Potomac, although he did make one appearance with the Columbus Clippers of the Triple-A International League.

On July 11, 2009, he pitched his first major league complete game against the Houston Astros, allowing only 2 runs on 9 hits.

[1] After recovering from a season-ending arthroscopic surgery in September 2009 and having a successful spring training, Stammen returned to the Nationals' rotation as their number 3 starter for the 2010 season.

[5] The following night he pitched 71⁄3 innings, allowing two runs on five hits, against the first place-Atlanta Braves, stopping a Nats' 5-game losing streak in a 7–2 win.

[4] On August 8, Stammen was assigned to the bullpen to make way in the starting rotation for Jason Marquis and Stephen Strasburg.

After a successful[peacock prose] spring training, Stammen made the Nationals' 2012 opening day roster, serving as a long reliever.

Stammen pitched four innings of perfect baseball: no hits, no runs, no walks, with three strikeouts for the win against division-leading Atlanta Braves.

[13] He split the season between the rookie-level Arizona League Indians, Double-A Akron RubberDucks, and Triple-A Columbus Clippers.

On June 9, 2019, facing his former team the Nationals, he gave up four consecutive home runs, to Howie Kendrick, then Trea Turner, then Adam Eaton, and then Anthony Rendon.

The injury caused Stammen to contemplate retirement, as the recovery timetable was set at four-to-six months without surgery.

[28] On January 30, 2024, Stammen re–joined the San Diego Padres organization as an assistant to the major league coaching staff and baseball operations department.

[30] Stammen grew up and still resides in North Star, Ohio,[31] a village about 11 miles (18 km) northwest of Versailles.

[33] Audrey and Craig Stammen were married on January 21, 2017, at Holy Angels Catholic Church in Dayton, Ohio.

Stammen's work with the United States Military is partially due to some of his college friends joining the Army and Marines.

In recognition of all his efforts to the military, he was the Major League Baseball recipient of the Bob Feller Act of Valor Award, in 2020.