He taught at the City of Basel Music Academy from 1968, influencing notable soloists including Nuria Rial and his son, Oliver Widmer.
[2] He then studied violin and voice at the Zürich Conservatory with Ria Ginster, and took master classes with Franziska Martienssen-Lohmann and her husband Paul Lohmann in Lucerne and Wiesbaden.
He performed in 19th century works including Dvorak's Stabat Mater and Verdi's Requiem, and in 20th-century oratorios such as Suter's Le Laudi, Honegger's Totentanz and Martin's Golgotha.
[3] Widmer toured in Europe, and also in Israel, Canada, Russia, Japan and the US, with conductors such as Rafael Frühbeck de Burgos, Michael Gielen, Paul Sacher, Wolfgang Sawallisch, Horst Stein and Jesús López Cobos.
Among his students were Marion Ammann, Miriam Feuersinger, Montserrat Figueras, Werner Güra, Nuria Rial, Anna Lucia Richter, and his son, Oliver Widmer.
[11] In 1988, he was a soloist in the first recording of François-Joseph Gossec's Requiem, with Bernadette Degelin, Greta De Reyghere, Howard Crook, the Maastricht conservatory chamber choir and Musica Polyphonica, conducted by Devos.