A native of Slavonski Brod, Zdravko Tomac began his political career in the Communist Party of Yugoslavia.

This served the SDP very well, which made Tomac into one of their most prominent members and thus gained enough nationalist credentials to improve its electoral chances in the long run.

With the SDP established as the top opposition party in Croatia, it had the upper hand in the negotiations that would lead to the 1998 pre-election pact with HSLS and victory at the 2000 Croatian parliamentary election.

What looked like a formality turned into a very unpredictable and increasingly vicious contest when Stjepan Mesić joined the fray.

This didn't have much effect and Mesić got easily elected, with Tomac's position within the party and the new government becoming increasingly marginalised.