Born in Arnsberg, Province of Westphalia, as the son of a senior government councillor, Siehr first studied medicine at University of Königsberg.
In Berlin, he decided to train his voice with Julius Krause and Heinrich Dorn.
[2] In 1863, Siehr made his debut at the Landestheater Neustrelitz [de] as Oroveso in Bellini's Norma.
At this latter theatre he starred in the world premiere of Jules de Swert's Die Albigenser in 1878.
He also sang Gurnemanz in the Privataufführungen [de] for the Bavarian King Ludwig II of Bavaria at the National Theatre Munich.