Johan Christian Tellefsen, Thomas's father, left Copenhagen in 1793 to study theology. At that time, he regularly participated in the social life of Copenhagen, performing and playing piano and violin. Music started to take up more and more of his time, and around 1800 he returned to Trondheim without completing his theology studies.
Johan Christian was deemed to have a very musical ear. In 1807, when the cathedral organist Johan Heinrich Berlin died, he was succeded by Tellefsen, who retained this post until his death, in 1857. After the proclamation of the Norwegian constitution, in 1814, the decision was taken to make Trondheim Cathedral the coronation church of Norway. This led to a greater role for music, especially in more prestigious church events. Tellefsen played the organ during the coronation of Carl III Johan in 1817, and also in later years, as organist and cantor, he played an important role in numerous national festivities.
From his letters home, it seems that Thomas Tellefsen also played the organ in the cathedral and composed small organ pieces for his father to perform during masses. He offered these pieces to his father in exchange for rare scores from his father’s collection.
The tradition of organ playing in Trondheim dates back to the Middle Ages. Historical documents prove the presence of an organist in the city already in 1319. A written source from 1593 confirms the existence of a pipe organ in the cathedral, and in 1637 an instrument was constructed there permanently. In 1869, a grand refurbishment of the cathedral was commenced; the main portion of it was finished over 100 years later, including the reconstruction of the western fronton. The predominant style is Gothic, but the older parts of the cathedral were built in Romanesque style. In 1988, the regalia were moved to the cathedral (today, they are kept in the Archbishop’s Palace, nearby), affirming its position as the coronation church.