He was the president of Protestant youth organisations from 1928, published songbooks, and was a leading member of the Confessing Church.

Born in Cannstatt, Riethmüller studied theology at the University of Tübingen and was especially influenced by Adolf Schlatter.

[1] In 1928, Riethmüler became director of the national Protestant organisation of young women (Evangelischer Reichsverband weiblicher Jugend) in the Burckhardthaus in Berlin-Dahlem, which was founded by Johannes Burckhardt in 1889.

[1] While he was president of the Evangelische Jugend [de] (Protestant Youth), he created their logo, the Cross on the Globe, in 1935.

[1] Riethmüller died on 19 November 1938 in Berlin and was buried at the Uff churchyard [de] in Bad Cannstatt.