Between 1852 and 1855, Johann Gottfried Wetzstein, the German consul in Damascus, and the Prussian king sponsored his travel to Syria, Mesopotamia and Persia.

He learned Armenian from the Mekhitarist Father Eduard Hurmuz on the island of San Lazzaro, which is part of Venice.

Petermann was interested in religious minorities such as the Samaritans, Druze, Mandaean, Yazidis, Parsees and Ahl-i Haqq.

Petermann published the first edition and Latin translation of two Mandaean writings, the Ginza and Sidra Rabba respectively, ("The Treasure", "The Great Directory") in his Thesaurus sive liber magnus.

[1] Petermann was a member of the Berlin Masonic Lodge, Friedrich Wilhelm zur gekrönten Gerechtigkeit.