As a composer, Uhl synthesized elements from neo-classicism, atonality, serialism and traditional tonal and contrapuntal idioms. His vibrant style combined technical sophistication and musical charm with wit and humour, rhythmic inventiveness, thematic development and advanced harmonic language. He wrote eight film scores, one opera, several choral works, and multiple symphonic and chamber music pieces. He wrote extensively for the clarinet, including educational material and works that are still common repertoire. His most famous educational pieces are the two volumes which comprise the 48 Studies (see below). His Divertimento for Three Clarinets and Bass Clarinet is one of the most performed works for the medium. Written in 1942 for clarinettists from the Vienna Philharmonic, it is a very demanding 3-movement work structured similarly to a conventional concerto.
Other works include a concerto for clarinet and orchestra (Konzertante Sinfonie for Clarinet and Orchestra) and a trio for clarinet, piano and viola (Kleines Konzert).
Two volumes of 24 studies each, first published in 1940 by Schott Musik International, were designed to familiarise the advancing clarinettist with some of the more difficult possibilities being written in modern instrumental music. This is stated by Uhl himself in a foreword to some, but not all editions. As such, they occasionally include intervals which require sliding over keys on the French system of clarinet, a technique that is generally frowned upon unless, as in these cases, it cannot be avoided.
The studies are characterized by their extensive use of neo-romantic chromaticism and rhythmic complexity. Occasionally viewed as less musical and more technical than most studies, some clarinetists consider it a second goal to bring out the musicality of each piece, which may be hidden behind technical complexities.
Uhl was assisted by Leopold Wlach of the Vienna Philharmonic Orchestra, who made suggestions and revisions throughout the writing process.