Pirmann was a four-year varsity player for Michigan State, although his senior season in 2007 was spent under a medical redshirt due to an injury sustained in preseason training and he returned for a fifth-year senior season in 2008. He played in 73 matches in four seasons, starting in 49 and notching one goal and 13 assists. During his time playing at MSU, the Spartans won their first two Big Ten conference titles in 2004 and 2008 and appeared in the NCAA Tournament in 2004, 2007 and 2008. Pirmann was a three-time Academic All-Big Ten selection and earned the team's Big Ten Sportsmanship Award in 2008.
Between 2005 and 2008, Pirmann played for two USL PDL squads in the fourth tier of the American soccer pyramid. Between 2005 and 2006, Pirmann was part of the Indiana Invaders organization, while 2007-2008 saw him play for the now-defunct West Michigan Edge.
After graduating from MSU with a bachelor's in communications and a master's degree in kinesiology with a concentration in coaching, Pirmann joined the Western Michigan University men's soccer team coaching staff as an assistant in 2009. In 2010, his Broncos team had one of the most successful seasons in its history, finishing second in the Mid-American Conference behind only the eventual national champion Akron Zips.
In 2011, Pirmann returned to Michigan State as an assistant coach. During his tenure there, the Spartans won the Big 10 tournament title in 2012 and reached the Elite Eight rounds of the NCAA Division I Men's Soccer Tournament in 2013 and 2014.
While maintaining his role at MSU, in 2013 Pirmann was named head coach of Detroit City FC (DCFC), which plays in a league that does not conflict with Michigan State's NCAA soccer season. In his first season at the helm, DCFC finished first in the NPSL's Great Lakes Conference and were ranked #1 nationally in the NPSL following an undefeated regular season. The team lost in the second round of the NPSL playoffs to eventual national semifinalist Erie Admirals S.C.
In 2014, DCFC finished second in its Great Lakes West Conference and did not make the playoffs.
In 2015, DCFC finished second in the Midwest Region, losing in the first round of the playoffs to AFC Cleveland.
In March 2015, DCFC announced that Pirmann, who has been nicknamed "Caesar" by DCFC's fans, would return as head coach for the 2015 season. The club's Northern Guard Supporters group offered a scarf for sale in the 2014-15 offseason with Pirmann's image surrounded by the phrase "HAIL CAESAR".
Pirmann made his U.S. Open Cup head coaching debut in 2014, as DCFC lost on penalty kicks to RWB Adria in the opening round of the 2014 tournament after a 2-2 draw in extra time.
His DCFC team lost in the 2015 tournament to the Michigan Bucks of the PDL 3-0, but beat the Bucks in a first round rematch in 2016 on penalty kicks before going on to lose to professional USL club Louisville City FC on penalty kicks in the second round.