Born in Wesel, Decken began his stage career in Rostock in 1892.

He was a member of the opera in Elberfeld (now Wuppertal) from 1893 to 1896, then moved Hofbühne in Stuttgarter , where he made his debut as Beppo in Auber's Fra Diavolo.

He was known for buffo parts, both for his singing as for acting with humour.

His parts included Gomez in Kreutzer's Das Nachtlager in Granada, Georg in Lortzing's Der Waffenschmied and other parts in Lortzing operas, David in Wagner's Die Meistersinger von Nürnberg, Mime in his Der Ring des Nibelungen, and Eisenstein in Fledermaus by Johann Strauss.

He remained in Stuttgart, working after World War I also as Spielleiter (stage director) until his death.