Kottmann, born 1932 in Zürich, started rowing aged 13 with Belvoir Ruderclub in his home city. For several years, he rowed with Rolf Streuli and various coxswains in the coxed pair event. They won the European Rowing Championships in 1954 in Amsterdam, in 1955 in Ghent, and came second in 1956 in Bled. They had qualified for the 1956 Summer Olympics in Melbourne but Switzerland was one of four countries to boycott the Games over the Soviet invasion of Hungary. At the 1958 European Rowing Championships in Poznań, Kottmann and Streuli won bronze.