He was one of the students of Zoltán Kodály. He greatly admired and became a young apprentice of Béla Bartók. His association with Bartók was for him both a blessing and a curse. He made great efforts to make Bartók's music more accessible, by arranging selected works for combinations of instruments, but this brought him more attention than did his own compositions.
For the most part his efforts were highly praised, both by Bartók and by colleagues. Bartók's Viola Concerto took two or three years of Serly's efforts to compile from sketches into a performable piece. It is now one of the most widely performed viola pieces.
One of Serly's most famous original works is Rhapsody for Viola and Orchestra. His work bringing Bartók's work to fruition has paid off in the sense that his works are often paired with those of his better known teacher, on recordings and in live performance.
Serly taught composition at the Manhattan School of Music in New York City (among other institutions) and was also a featured composer/conductor with the Danish radio orchestra. A number of his students went on to have notable careers, including composers Manny Albam, Jerry Bilik, and Mark Bucci. Serly also taught orchestration to Carlyle W. Hall Sr, a trumpet player and arranger for Tommy Tucker's band, who went on to orchestrate the Broadway hit musical Man of La Mancha, as well as Cry for Us All (a musical version of Hogan's Goat), Come Summer, and several others.
The American objectivist poet, Louis Zukofsky, wrote a dedicatory poem to Serly, published in the avant-garde magazine, Blues, in February 1929.
As a violist, Serly was chosen to be part of the NBC Symphony Orchestra for its debut season, 1937-1938, the same orchestra conducted by the legendary Arturo Toscanini. He left after the first season to concentrate on compositional activities.
In the course of rethinking the major developments in harmony found in the work of Stravinsky, Milhaud, Prokofiev, and Vaughan Williams as well as Bartók and other composers, Serly developed what he referred to as an enharmonicist musical language. In his book Modus Lacscivus (1975) he explored a set of 82 basic tertian chords. Serly titled several of his later works as being "in modus lascivus," including sonatas for violin, viola, and piano. (The 1973 edition of his piano sonata misspells the term "modus lascivus" on the cover, copyright, and title pages, putting the "s" and "c" in reverse order.) His Concertino 3 X 3 uses this compositional system, but is most memorable for its formal structure: it consists of nine movements, the first three for piano solo, the second set of three movements for orchestra without piano, and the final set combining the previous sets, played simultaneously.
- Symphony No. 2 in Two Movements for Woodwinds, Brass, and Percussion
- Rhapsody on Folk Songs Harmonized by Béla Bartók for Viola and Orchestra (1946–48)
- Concerto for Viola and Orchestra (1929)
- Concerto for Violin and Wind Symphony (1955–58)
- Concerto for Two Pianos and Orchestra (1958)
- Concerto for Trombone and Orchestra (1951)
- Piano Sonata No. 1 in "Modus Lascivus" (1946)