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Guthman started his musical career at the age of nine and studied classically for the first 15 of his playing years. After attending Portland State University, he performed short stints in the 1980s as the “youngster” with the Dorsey Brothers Big Band, the Stan Kenton Orchestra, the Don Ellis Orchestra and with Louis Bellson.
Since the early 1990s, Guthman has performed for audiences throughout the world with his “Tribute to Harry James”, “Trumpet Greats”, and “Salute to Swing” in concert halls, jazz festivals and with Symphony Pops.
From 1999-2001, Gary starred in the award-winning Big Band Musical Theatre production of “Forever Swing” which toured in the United States and Canada for nearly 24 months.
In the summer of 2004, he presented his Big Band production entitled "Swingmatism" at the Vancouver International Jazz Festival.
In 2008, Guthman moved to Warsaw, Poland where he resides currently. Since that time, he has performed over 300 concerts throughout Poland and Central Europe. In Poland, due to his extensive "Swing", "Big Band" and "Symphony Pops" concerts, he has in some circles been called Poland's "King of Swing".
In 2009, Guthman recorded with Włodek Pawlik on the award winning Poland film "Rewers" (Reverse).
In 2010, he began the "Solar Eclipse" project with his new jazz quartet: Filip Wojciechowski - piano, Pawel Panta - Bass, Cezary Konrad - Drums. In September 2011, "Solar Eclipse" was released on Polish National Radio label. Gary Guthman is the first American-born jazz musician to ever have a solo CD produced by Polish National Radio in its 90-year history.
- Pressley, Nelson (February 15, 2001). "'Forever Swing': Keeping Time; Musical Captures an Era in a Bright Net of Notes". Washington Post. Retrieved 12 December 2010.