[1] He was a pioneer of electronic music Kessler was born on 25 September 1937 in Zürich.
He studied literature at the Universities of Zurich and Paris, followed by composition studies with Heinz Friedrich Hartig, Ernst Pepping and Boris Blacher at the Hochschule für Musik Berlin.
In 1965 he founded his own electronic studio and became a member of the Gruppe Neue Musik Berlin.
[2] His students include Wolfgang Heiniger, Max E. Keller, Bettina Skrzypczak, René Wohlhauser and Thomas Chr.
Together with Gérard Zinsstag he founded the Tage für Neue Musik in Zürich and with Wolfgang Heiniger the Festival ECHT!ZEIT in Basel.