The polls conducted by Ipsos polling agency and published by state television station HRT, said Zoran Milanovic won nearly 78% of the vote compared to his challenger Dragan Primorac, who gained around 22%.
Milanovic comfortably won the first round of voting on Dec. 29 but failed to reach an absolute majority, forcing a run-off between him and second placed Dragan Primorac.
Milanovic, 58, is an outspoken critic of Western military support for Ukraine in its war against Russia. He is the most popular politician in Croatia, and is sometimes compared to U.S. President-elect Donald Trump for his combative style of communication with political opponents.
Official results were expected later in the evening.