After qualifying as a notary and land registrar, Thomas Weltert worked in the private sector as a legal consultant in Zurich and later as an investigating judge for white-collar crime and first public prosecutor a.i. of the Canton of St. Gallen. He also worked as an appeal judge (senior judge) at a federal court. He also taught at the Academy of Public Prosecutors at the University of Lucerne. Finally, he worked for Raiffeisen Switzerland Cooperative Special Tasks / Investigations.

Efficiency, straightforwardness, high flexibility, combined with pragmatism are the characteristics of his mandate management.