From 1981 - 1982, Fleissner was assistant to the artist couple Mario and Marissa Merz. From 1986 - 1987, he studied at the Academy of Applied Arts of Vienna and from 1975 - 1993 at the Academy of Fine Arts, Vienna. The former punk musician considers himself to be a painter, graphic artist, sculptor and object artist.
In his sculptural works, he tackles the throwaway society and waste objects. For his works, he uses material waste from all around, changes different things that were already there into something new and thus opens a new perspective and room for interpretation manœuvers. Waste material of commodity culture is reworked and re-assembled. In his sculptural work, he is searching for new approaches. He is an all-round artist. In his assemblies, sculptures and installations, the artist tries to bridge the gap between old and new.
Fleissner's sculptures were exhibited in 1991 at the Viennese Secession, in 1992 in the framework of "steirischer herbst" and in 1994 at the Museum of Modern Art, New York. In 2001, his works were shown at the Neue Galerie and in 2002, at the Stadtmuseum Graz.