He graduated at Zagreb's Law School. In the early 1970s, due to his participation in the Croatian Spring movement, he spent one year in jail in Stara Gradiska.
In 1990 he joined the Croatian Democratic Union (HDZ) party, becoming a senior official.
After Croatia's first multiparty elections in 1990, Mesic was appointed Croatia's first prime minister. That year the Croatian Parliament appointed him to the Presidency of Socialist Yugoslavia (SFRJ).
In July 1991, he became the chairman of the SFRJ Presidency, resigning from the post in December that year.
He was elected Croatian Parliament speaker in September 1992, from which post he was replaced in May 1994 over his public criticism of the policy of the ruling HDZ, notably towards neighbouring Bosnia-Herzegovina. He left the HDZ and formed the Croatian Independent Democrats (HND).
After rifts in the HND, Mesic joined the Croatian People's Party (HNS), becoming a senior official.
The HNS nominated him as its candidate for Croatia's third presidential election in January 2000, which he won in the runoff.
Backed by eight parties, Mesic ran in Croatia's fourth presidential election this January, defeating the HDZ's Jadranka Kosor in today's runoff for a second five-year term.
Mesic is married, with two children.