Szeemann was born in Bern. He studied art history, archaeology and journalism in Bern and Paris, and in 1956 he began working as an actor, stage designer and painter, as well as doing one-man shows. He started creating exhibitions in 1957. From 1961 to 1969 he was curator of the Kunsthalle Bern.There he organised an exhibition of works by the "mentally ill" from the collection of the art historian and psychiatrist Hans Prinzhorn in 1963, and the exhibition "When Attitudes Become Form" in 1969. In 1968 he gave Christo and Jeanne-Claude their first opportunity to package an entire building: the Kunsthalle.After leaving the Kunsthalle he founded the "Museum of Obsessions" and the Agentur für Geistige Gastarbeit ("Agency for Spiritual Migrant Work"). In 1972 he was the youngest artistic director at documenta 5 in Kassel. He revolutionised the concept: conceived as a hundred-day event, he invited the artists to present not only paintings and sculptures, but also performances and "happenings". In 1980 he co-hosted the Venice Biennale, where he created the "Aperto" exhibition for young artists. He was later among the few to curate the Biennale twice, in 1999 and 2001. From 1981 to 1991, he was the sole curator of the Kunsthaus Zürich. He also curated the international exhibition Einleuchten, the inaugural exhibition at the Deichtorhallen in Hamburg, in 1989. In 1982 Szeemann commissioned a three-dimensional reconstruction of Kurt Schwitters's Hannover Merzbau (as photographed in 1933) for the exhibition "Der Hang zum Gesamtkunstwerk" in Zürich the following year. It was built by the Swiss stage designer Peter Bissegger and is now on permanent display in the Sprengel Museum in Hanover. Szeemann played a key role in shaping the architecture faculty at the Università della Svizzera italiana, the first university in Italian Switzerland, for the first six years after its founding in 1996. From 1961 until his death, Szeemann belonged to the artists' group "Collège de 'Pataphysique'", from 1997 he was a member of the Akademie der Künste in Berlin, and in 2000 he was awarded the Max Beckmann Prize. Szeemann was married to the artist Ingeborg Lüscher, and lived in the village of Tegna in Ticino, Switzerland. He died in Ticino in 2005.