From 1958 to 1964 was lecturer at the Faculty of Heidelberg and the period 1964–1965 he worked as a researcher at the Max Planck Institut.
In 1969 he was elected professor of law at the University of Thessaloniki, but was not permitted to teach by the ruling military regime.
Just before his murder, Alecos Panagoulis publicly accused Tsatsos of close collaboration with the military regime, including filing damning reports on students involved with the resistance movement.
At the same time he was a full professor of German and International Public Law at the University of Hagen.
During the period 1993–1994 he served as unpaid adviser to the Prime Minister, and in 1994 he was elected MP of the Panhellenic Socialist Movement.