He completed his education by attending master classes with Gustav Leonhardt, Anton Heiller, Luigi Ferdinando Tagliavini, Marie-Claire Alain, Cor Kee among others.
[1] He began teaching improvisation and score playing at the Vienna Musikhochschule and continued with a six-year assistant to Nikolaus Harnoncourt at the Mozarteum Salzburg.
For more than two decades, Sonnleitner led the master classes for keyboard instruments within the Innsbrucker Festwochen der Alten Musik.
[2] Margarete Kopelent, Marie-Louise Dähler, Yasunori Imamura and Naoki Kitaya were among those who studied with Sonnleitner, and he taught courses to artists like Oscar Milani, Christine Schornsheim and Gudrun Schaumann.
He has published his teaching and research activities in the field of performance practice (especially with regard to historical tempo and metronome indications) in a series of essays and together with the musicologist Clemens-Christoph von Gleich in the study work Bach: Wie schnell?