Jaroslav Vožniak studied at the Academy of Arts, Architecture, and Design in the studio of Karel Svolinský (1951−1954) and at the Prague Academy of Fine Arts under Vladimír Silovský (1954−1959). By 1957 he was exhibiting his works and he had his first solo exhibition in 1964.
He was a member of the legendary Šmidrové group, along with Bedřich Dlouhý, Karel Nepraš, Čestmír Janošek and others, which combined campaigning for the right to artistic freedom with an aesthetics of strangeness as an alternative to structural abstraction. Vožniak was a leading representative of the 1960s generation. He was well known for his specific version of titillating pop-art that was related to surrealist imagination and hyperrealism.
After a very brief phase during which he also tried his hand at the abstract art then in vogue, a narrative element returned to his works. The return to real shapes was confirmed in the years 1963−1964. Complex vegetative accretions forming disintegrating shapes started to appear in his paintings and evidently surrealistic and chiefly erotic symbols started to be used alongside the idols of pop art. From the mid-1960s he began to create assemblages that had great inner tension in which Vožniak linked abstract painting with a naturalistic three-dimensional object. In the 1960s he created an important series of objects of manneristically decadent bizarreness that he underlined by a largely red polychrome in which he incorporated fragments of curios and valuable antiques to create imaginary reliquaries. In the 1970s Vožniak lived in seclusion, creating large-scale works of smooth painting with surrealist symbolism. In the subsequent decades he gradually returned to assemblages, and his oeuvre concludes with a series of Pollockesque poured abstractions.