Michael Mantler was born in 1943 in Vienna, Austria, where he studied trumpet and musicology at the Academy of Music and Vienna University. In 1962 he went to the USA to continue his studies at the Berklee School of Music in Boston.
He moved to New York in 1964 and started playing trumpet with Cecil Taylor and others. During that period he was also involved in the formation of the Jazz Composer's Guild, a collective of musicians and composers, struggling for better working conditions and opportunities to present their new music without compromise. Together with Carla Bley he formed a large jazz orchestra to perform new compositions, resulting in their first recording Communication.
After the Guild discontinued its activities, he toured Europe twice during 1965/66 with the Jazz Realities Quintet, featuring Steve Lacy and Carla Bley. He then established the Jazz Composer's Orchestra Association, a non-profit organization to commission, perform, and record new compositions for jazz orchestra.
He recorded a double album of his music during 1968 with the Jazz Composer's Orchestra and soloists Cecil Taylor, Don Cherry, Roswell Rudd, Pharoah Sanders, Larry Coryell, and Gato Barbieri. Some of this music was also performed during the Long Concerts at the Electric Circus in 1969.
He appeared as trumpet player on Carla Bley's A Genuine Tong Funeral, recorded by Gary Burton, and also on Charlie Haden's Liberation Music Orchestra album (1969).