As early as 1836, Thiersch had become interested in the Catholic Apostolic Church ("Irvingism"). In 1847 he converted, and in 1850 resigned his professorship to dedicate himself as a minister in that church.
Thiersch's fascination with the Catholic Apostolic Church ("Irvingism") dates back to 1836. He formally joined the church in 1847 and left his academic position the following year to pursue a career as a clergyman.