Tritsis was born in 1937 in Argostoli, Kefalonia. His family moved to Athens after the 1953 earthquake. Tritsis studied architecture at the National Metsovio Polytechnic school graduating in 1959. At that time he also took up athletics and was a champion at the decathlon. In 1960, he left for the US to continue his studies on a scholarship. He returned to Greece in 1963.
Tritsis became involved in politics after the restoration of democracy in 1974 joining PASOK. After PASOK won the 1981 elections, Tritsis became Minister of the Environment. In 1986 he became Minister of Religion and Education. However, in 1988 Tritsis fell out with PASOK leader, Andreas Papandreou, and left the party.
On October 14, 1990, Tritsis was elected Mayor of Athens with conservative New Democracy support, defeating actress-activist Melina Mercouri. During his term in office, he visited Baghdad after the first Iraq conflict in 1991 and, on February 10, reported that, contrary to Western reports, the city had been pretty much randomly bombed.