He is mainly known for founding a number of prominent Croatian orchestras and for his longtime service as the conductor of the Radio Zagreb Dance Orchestra (present-day Croatian RadiotelevisionBig Band Orchestra).
Prohaska was born in Zagreb and he first began learning the violin at a children's music school in Zagreb. He went on to enrol at a secondary music school where he was educated as a contrabass player and graduated in 1951, before continuing his studies at the Zagreb Music Academy and graduating in 1956 from the music teaching department. Since the mid-1950s until the late 1980s Prohaska was a contrabass player with the Zagreb Philharmonic Orchestra, the Radio Zagreb Symphony Orchestra, the Yugoslav Radio Orchestra, the Zagreb Jazz Quartet and many other musical ensembles. He was also the director of the Zagreb Festival of Popular Music (Zagrebfest) from 1967 to 1969.