Iran’s judiciary chief Ebrahim Raisi emerged as the winner of Friday’s presidential election after the three other candidates conceded before counting of votes was completed, according to local media.
Former central bank governor Abdolnasser Hemmati, seen as Mr Raisi's main rival, issued a letter congratulating him on Saturday morning.
"I hope your government, under the leadership of Supreme Leader Ayatollah Ali Khamenei, will bring comfort and prosperity to our nation," Mr Hemmati said.
Mohsen Rezaei, a former commander of the Islamic Revolutionary Guard Corps, also congratulated Mr Raisi, while Amirhossein Ghazizadeh Hashemi, the first deputy speaker of the Iranian Parliament, hailed him as ‘the nation’s chosen one’, the semi-official Fars news agency reported.
President Hassaan Rouhani congratulated the election winner without naming him, saying the election outcome was clear.
“I can’t officially congratulate the winner, so I will defer my congratulations,” Mr Rouhani said in a televised speech before the release of official results. “But it’s clear who the president-elect is."
Mr Raisi, hard-line protege of Mr Khamenei, had been tipped to beat the three candidates left in the race after three others withdrew in the past week.
The official turnout for the election was expected to be a historic low amid voter apathy and anger over the limited field of approved candidates that sparked for an election boycott. Polls closed early on Saturday after 19 hours of voting, with the official results expected as early as midday.
Just over 12 hours into voting, nationwide turnout had reached 37 per cent, the Fars news agency reported, as overseas Iranians also cast their ballots in Iraq, Kuwait, Lebanon and elsewhere.
Pre-election polling by the Iranian Students Polling Agency found only 40 per cent of the 59.3 million eligible Iranians intended to vote.
No presidential race since the republic was founded in 1979 has had a turnout below 50 per cent.
Supreme Leader Ayatollah Ali Khamenei urged people to come out and vote after casting the ceremonial first ballot on Friday morning.
"Each vote counts ... come and vote and choose your president ... this is important for the future of your country," he said after casting his vote in the capital Tehran.
After a two-hour extension following calls from some media and the campaigns of candidates, voting officially closed at 2am on Saturday.
A run-off was scheduled for June 25 if no clear winner emerged in Friday's vote.
The elections faced early difficulties, with reports of malfunctioning electronic voting machines at some polling locations in Tehran and other places across the country, and a shortage of paper ballots at others.
The governor of Tehran, Anoushirvan Mohseni Bandpay, said 79 polling stations in the capital faced technical issues.
Voting also took place around the world at Iran's various consulates and embassies.
Foreign Ministry spokesman Saeed Khatibzadeh said there were 133 diplomatic missions and 234 polling stations abroad where Iranians could vote. Singapore, Yemen and Canada were the only countries where expats were not able to vote.
In the UAE, voting took place at the Iranian consulate in Dubai.
The polling opened 8am local time. Mirroring the low turnout in Iran and other locations around the world, handfuls of Iranians filtered in and out of the consulate, barely having to wait to cast their ballots. Those that showed up were seemingly conservative older voters and mostly men.
Big-name politicians went to the polls as well, including reformist leader and former president Mohammad Khatami. Mr Khatami's images and name are banned from being published by Iranian media because of his support for the protests against alleged fraud in the 2009 presidential election that gave Mahmoud Ahmadinejad a second term.
Foreign Minister Javad Zarif used the polling station in Antalya while on a diplomatic trip to Turkey.
Mr Raisi cast his ballot in Tehran in the morning. Moderate candidate Abdolnasser Hemmati and his wife also cast their ballots early.
Mr Ahmadinejad, who called for an election boycott after being disqualified from running this year, confirmed that he would not be voting. He published a video in which he said he would not be supporting any of the candidates and calls the elections a "sin" that ignores the will of the people.
The election cycle was largely dominated by voter apathy, and Iran's attempts to revive its nuclear deal with world powers and jump-start the struggling economy were both issues seen as failures of President Hassan Rouhani's administration.
During debates leading up to the election, the candidates used much of their time to blame Mr Rouhani for government failures over the past eight years.
Despite efforts by the candidates to enthuse the electorate, the ideologically narrow field of candidates led many Iranians to sit out this election cycle.
Traditionally, high voter turnout has resulted in the election of reformist and moderate candidates. Low voter turnout favours hardline candidates.
This year, the combination of a list of nearly all hard-line and conservative candidates along with deep-seated voter apathy is likely to hand a win to Mr Raisi.
If elected, he would be the first serving Iranian president to be sanctioned by the US government even before entering office.
He was sanctioned for his involvement in the mass execution of political prisoners in 1988, as well as for his time as the head of Iran’s internationally criticised judiciary.
Prior to election day, Mr Raisi's level of support was polling at 63.7 per cent among those who said they would be voting.