Demmer was baptized on 6 August 1772 in the Cologne parish St. Maria im Pesch [de] under the name Christian Joseph.
[1] He was a brother of Joseph and Carl Demmer and began his artistic career on 13 December 1780 as a choir singer at Cologne Cathedral.
He celebrated his greatest successes in the role of Ober-Seneschall in the singspiel Jean de Paris by François-Adrien Boieldieu, which was performed for the first time on 28 August 1812 in the Theater am Kärntnertor.
Ignaz Franz Castelli writes in his memoirs: Two Demmer brothers were employed as singers, one at the court opera, the other at the Theater an der Wien; they played all the chevaliers, they looked so alike, and had so much the same manners and so much the same language that it was almost impossible to tell them apart.
[6]According to the Viennese artist directory by Franz Heinrich Böckh, "Demmer Christ, K-k lived (Hof-Opern-Sänger" 1821) "An der Wien No 38.