The graphic artist taught himself his artistic skills. From the early 1960s, he dealt with the word and the picture from an artistic point of view and was considered as one of the most important pioneers and representatives of "visual poetics" worldwide. Starting from "concrete poetics", he developed a pictorial language in its own right from 1961 and dedicated himself to the problems of surface grammar. Ontological concepts and relations that make up his major group of works play an important role. From 1963, he was in contact with the "Wiener Gruppe". In the same year, he took part in the exhibition Schrift und Bild in Amsterdam and Baden-Baden. His first Austrian solo exhibition took place in 1970 in the Galerie nächst St. Stephan, Vienna. Then he was engaged with the futurists' works and the œuvre of French symbolist Stéphane Mallarmé. Gappmayr also dealt with Piet Mondrian's work, especially with philosophical and human claims that inspired him.
From the mid-1970s, the number appeared as a new element in his visual poetry. In 1979, he started to transfer his graphic works to the space. For these “text pictures”, he used adhesive letters and a tape. Around 1989, he created his first “text pictures” - wooden parts covered with canvas - that provided each text with a space of its own. In the 1990s, colors started to play a greater role than before. From time to time, the artist also worked with photography. Besides time and space, surface and the image or picture as such became his preferred subjects. Gappmayr's œuvre comprises approx. 2000 individual works.
In 1969, the artist took part in the Venice Biennale. In 1965, he exhibited at the Institute of Contemporary Arts in London, in 2002, at the Sharjah Art Museum in the United Arab Emirates, and in 2001, at the Grazer Kunsthaus, as well as at the Gallery Sonja Roesch, Houston. In parallel with many exhibitions in Austria and abroad, he wrote many theoretic papers. In 1988, the Republic of Austria awarded him the title "professor", in 1995 he was awarded the Art Prize of the Tyrol.