Secretary to Duke George of Saxony, Emser was ordained a priest in 1512. It is possible that a young Martin Luther was among his students at the University of Erfurt. Emser first sided with the Reformers, but opinions expressed by Luther at Leipzig brought their friendship to an end.

Emser wrote 8 polemical tracts against Luther in 1520 to 1521. In 1527, Emser published a German translation of the New Testament from the Vulgate, with annotations. It was meant to counter Luther’s translation, but it was really a revision of Luther’s own work.