Retired academic Kais Saied is set to become president of Tunisia, exit polls suggest.
The poll said the law professor, 61, had secured 76% of votes. No official results have yet been published.
He was up against media mogul Nabil Karoui, 56, who campaigned from prison after being arrested on charges of money laundering and tax fraud.
He denies the charges and officials have warned he may appeal, arguing he has not been allowed a fair campaign.
After the exit polls were released, Mr Saied appeared in front of jubilant supporters in Tunis and thanked “young people for turning a new page” in Tunisia’s history.
“We will try to build a new Tunisia. Young people led this campaign, and I am responsible for them,” he said, flanked by his family.
Mr Karoui, who was freed by a court order just four days ago, came second in the first round of voting, with 15.6% of the vote to Mr Saied’s 18.4%.