A student of Paul Hindemith, Etler is noted for his highly rhythmic, harmonically and texturally complex compositional style, taking inspiration from the works of Bartok and Copland as well as the dissonant and accented styles of jazz.
Though he played with the Indianapolis Symphony in 1938, he abandoned his orchestral life shortly thereafter to focus on his increasingly successful compositional career (which earned him two Guggenheim Fellowships during this period). In 1942 he joined the faculty at Yale University as conductor of the university band and instructor of wind instruments, where he began his studies with Hindemith. He also taught at Cornell University and University of Illinois before accepting a position at Smith College, which he held until his death.
Notable works include his two woodwind quintets (from 1955 and 1957), a bassoon sonata, the 1963 "Quintet for Brass Instruments", and "Fragments" for woodwind quartet.
Etler is also the author of Making Music: An Introduction to Theory, an introductory-level theory text published posthumously in 1974.