Conservative political outsider Kais Saied was given a sweeping mandate to be Tunisia's next president, thanks largely to young people who flocked to his side.
The country's electoral commission confirmed on Monday that Mr Saied won Sunday's runoff with 72.71 per cent of the votes.
In a contest that reflected Tunisia's shifting post-revolution political landscape, Mr Saied, an independent, scooped up more than 2.7 million votes, sweeping aside his rival, charismatic media magnate Nabil Karoui who garnered one million.
"He was elected very comfortably," political scientist Selim Kharrat said.
Mr Saied won double the votes of all 217 politicians combined who were elected in October 6 general elections.
This win "is a message to parliament," Mr Kharrat said. "Voters have opted for a plan to clean up politics, fight corruption, and give more power to local entities."
The electoral commission ISIE reported the turnout was at least 58 per cent, a steep rise from the first round.
Mr Saied, a retired law professor with a rigid and austere demeanour that earned him the nickname "RoboCop", was carried to victory by young voters.
Around 90 per cent of 18 to 25 year olds voted for Mr Saied, estimates by the Sigma polling institute showed, compared with 49.2 per cent of voters over 60.
In his first reaction, Mr Saied thanked the country's young people "for turning a new page", and vowed to try to build "a new Tunisia".
Thousands of people took to the streets of the capital Tunis late on Sunday to celebrate Mr Saied's victory, honking horns and singing the national anthem.
"Kais Saied, voice of the people," a gathered crowd chanted. "Long live Tunisia!"
The runoff pitted Mr Saied against another newcomer, businessman Mr Karoui, who has been dubbed Tunisia's "Berlusconi" after the former Italian prime minister.
Mr Karoui had been jailed for the majority of the campaign, only walking free on Wednesday after more than a month behind bars on suspicion of money-laundering. He has dismissed the charges as politically motivated.
Mr Saied and Mr Karoui both trounced the old guard in a September 15 first round, highlighting voter anger over a stagnant economy, joblessness and poor public services in the cradle of the Arab Spring.
The country's high unemployment rate disproportionately affected young graduates, fuelling their calls for political change.
The poll, Tunisia's second free presidential election since its 2011 revolt, followed the death of president Beji Caid Essebsi in July.
Tunisians took to social media, many voicing pride in a successful democratic process.
"Congratulations to Tunisia … for showing a continued commitment to resolving differences via peaceful transitions," said H.A. Hellyer, a senior fellow at the Royal United Services Institute in London, in a tweet.
The Ennahdha party, which won the most seats in parliament in the general elections, had called on supporters to back Mr Saied.
While the candidates were both seen as anti-establishment figures, the contrast between them was stark.