Weissmann went to University of Zurich and obtained his MD in 1956 and Ph. D. in Organic Chemistry in 1961. In 1978, Weissmann co-founded the biotech company Biogen in Geneva. Biogen is considered one of the pioneers of the biotechnology industries. Weissmann was director of the Institute for Molecular Biology in Zurich, President of the Roche Research Foundation and co-founder and Member of the Scientific Council of Biogen. He is currently Chairman of the Department of Infectology, Scripps Florida.