From 1983 to 1992, Walliser worked as a solo repetiteur at the Deutsche Oper Berlin with a focus on Wagner, Strauss, and modern music (including premieres). In addition, he worked as an assistant to Gary Bertini in Frankfurt am Main in 1987/1988 and to Giuseppe Sinopoli in Berlin, Rome, Taormina, and Milan from 1990 to 1994. Since 1992, he has been a professor of score and piano reduction playing at the UdK Berlin. From 1993 to 2003, he organized lieder evenings and chanson programs and released CDs.
From 2001 to 2006, Walliser also worked as a pianist and coach at the Komische Oper Berlin. From 2003 to 2006, he was co-conductor with Johannes Kalitzke at the Steirischer Herbst/Opera Bastille, the Staatsoper Unter den Linden, and the Theater an der Wien (including premieres of works by Bernhard Lang and Hans Zender). Since 2000, he has performed as a pianist with major Berlin orchestras and the Deutsche Oper Berlin, as well as a harpsichordist (playing basso continuo) with the Kammerorchester Berlin. He also collaborates with various singers.