He earned a Bachelor of Music degree in Theory and Composition in 1977 and a Bachelor of Arts degree in Music Education in 1978, both from Saint Olaf College in Northfield, Minnesota. In 1983 he completed a Master"s degree at the University of Iowa in Trombone Performance. He completed his doctorate Musical Arts in Instrumental Conducting in 1995, also from the University of Iowa.
Currently, he is a professor of music at Saint Olaf College and conductor of the Saint Olaf Band. Mahr teaches courses in composition, music education, and conducting. He is Past President of the North Central Division of the College Band Directors National Association (1999–2001) and has served on the board of directors of the National Band Association and the Minnesota Band Directors Association.
Mahr remains active as a guest conductor and clinician, in demand as a guest composer/conductor on over 35 college and university campuses.
Mahr"s compositions have been performed by ensembles worldwide, and many have been published. The first recipient of a commission from the American Bandmasters Association Commissioning Project, Mahr continues to be commissioned by universities, colleges, high schools, state band associations and community groups nationally.
Notable commissions include works for the Music Educators National Conference, the Kappa Kappa Psi/Tau Beta Sigma National Intercollegiate Band, the 50th anniversary of the American School Band Directors Association and the United States Air Force Band. Mahr conducted the Massachusetts All-State band at Symphony Hall in Boston (2000).
This performance featured his outstanding original score, "Endurance," based on Shackleton"s attempt to reach the South Pole.
In 2010, Mahr was a clinician for the 50th anniversary of the WELS National Band Festival in Onalaska, Wisconsin at Luther High School. He composed the piece "Tres Solas" (which has not been released yet) specifically for this event. Mahr is perhaps best known for his compositions for concert band, including the highly descriptive tone poem "The Soaring Hawk" (1990), and "Endurance" (1991) (commissioned by the American Bandmasters Association Commissioning Project).