Hartmann worked for two years in the advertising department of Bally Shoes and then attended the Zürich Kunstgewerbeschule (1932–36). He shared an atelier with Hans Fischer in Berne, then started his own in 1938; later on, Hartmann moved to Köniz. He was a designer of many effective logos and posters for important firms and institutions, such as Swiss Railways, the Swiss National Council for Road Safety, and Swissair. For the Swiss PTT he designed several stamps. He received a Certificate of Merit from NY ADC. The Swiss Federal Department of the Interior granted him five awards for posters and three in a competition for books and stamps to promote an anti-malaria campaign. He designed posters and folders for the Ministry of Transport. He had the unique visual power and clarity that allowed him to come up with posters that could work well without text (practical in his country, with its four languages). Hartmann also designed the cover for Graphis #28, 1949.