From 1978 to 1983 he attended the Musikgymnasium Schloss Belvedere [de] in Weimar.
Afterwards he studied at the Hochschule für Musik Franz Liszt, Weimar with Axel Schmidt, solo English horn player in the MDR Leipzig Radio Symphony Orchestra.
Already during his studies Sieberth was a substitute at the Staatskapelle Weimar, in 1988 he graduated with a diploma.
He is also a lecturer for oboe at the Musikgymnasium Schloss Belvedere (Weimar) and in the master classes of the Landesmusikakademie Sondershausen [de] tätig.
In 2008 he founded the Trio Saphiro together with the Frankfurt harpist Bettina Linck and the Meiningen concert soprano Anna Gann.