With over 99 per cent of votes counted, Milanovic scored 52.7 per cent of the votes in Sunday's presidential runoff against the incumbent President Kolinda Grabar-Kitarovic who got 47.3 per cent.
A total of 11 candidates competed in the first round of presidential election on December 22, 2019.
Milanovic, who was running as the candidate of the Social Democratic Party (SDP) and several other center-left parties, won in the first round with nearly 30 per cent of the votes, while Grabar-Kitarovic, a conservative candidate supported by the ruling Croatian Democratic Union (HDZ), came second with almost 27 per cent. Since none of the candidates had obtained over 50 per cent of the vote, a second round with the top two candidates was held on Sunday.
According to the State Electoral Commission, nearly 55 per cent of over 3.8 million eligible voters had cast their ballots in the presidential runoff.
The Croatian president is elected once every five years.
In his victory speech on Sunday night, Milanovic promised that he will listen and represent all citizens.
Grabar-Kitarovic congratulated Milanovic on his victory. "I am giving my hand out to Zoran Milanovic to show the voters how a peaceful transition of the government looks like," she said.
Milanovic, 53, served as Croatian prime minister from December 2011 until January 2016.
( With inputs from IANS )