Social Democratic Party (SDP) leader Zoran Milanovic announced on Monday that he would not run for another term as the party's chief.
Milanovic made the announcement at an extraordinary press conference after Sunday's early parliamentary election at which his party lost to the Croatian Democratic Union (HDZ).
He said that the SDP's bodies would call a party election within the next 150 days as required by the party's statute.
Milanovic noted that the turnout for Sunday's vote was lower than ever, which he said played in favour of the rival bloc. "It's a fact that we should accept rather than philosophise about it," he added.
Milanovic has been at the SDP's helm since 2007, and the SDP has not won a parliamentary election since 2011.