Titius was born in Konitz, Royal Prussia to Jakob Tietz, a merchant and council member from Konitz, and Maria Dorothea, née Hanow. His original name was Johann Tietz, but as was customary in the 18th century, when he became a university professor, he Latinized his surname to Titius. Tietz attended school in Danzig (Gdańsk) and studied at the University of Leipzig (1749-1752).