Johannes Schlaefli began his musical career as an oboist. He learnt conducting, for the most part, autodidactically. He received important impulses Erich Schmid, Mario Venzago, Kirk Trevor and Leonard Bernstein amongst others.
Johannes Schlaefli has guest-conducted such orchestras as the Tonhalleorchester Zürich, Zurich Chamber Orchestra, the Orchestra della Svizzera Italiana, the Indianapolis Chamber Orchestra, the Prague Chamber Philharmonic, Ostrava's Janacek Philharmonic, the West Bohemian Symphony Orchestra, the Orchestra Sao Paulo, the Hong Kong Sinfonietta and so on.
Schlaefli directed the Basel Chamber Orchestra for 15 years and played a significant part in its development. In 1984 he took over the direction of both the orchestral formations of the Zurich colleges. He has been the Chief Conductor of Berne Chamber Orchestra since 1995.
Johannes Schlaefli has been a teacher of many years with the International Conductor's Course of the Symphonic Workshops in the Czech Republic. He has supervised orchestral conductor training, as a major subject teacher, at the Zurich School of Music since 1999.