He was a prolific composer of madrigals and instrumental music, and was renowned as one of the finest organists in Italy in the late 16th century; he was also the principal teacher of Adriano Banchieri.
The major influences on Guami's sacred music style are from Willaert, his teacher at St. Mark's, and Cipriano de Rore, and later from Lassus; indeed the two composers may have been friends since they served together in Munich and evidently traveled together.
In his secular music he was most progressive, using an unusual amount of chromaticism and modulation to distant keys, undoubtedly influenced by Nicola Vicentino.
The canzonas are in the up-to-date Venetian style, antiphonal, ornamented, and using starkly different thematic material in different sections; however they contain an unusual level of motivic development for pre-Baroque music.
Guami was also important as a teacher, providing instruction to composers such as Adriano Banchieri, one of the key figures in the transition to the Baroque style.