TEHRAN—As Iranians prepare to head to the polls on Friday, the only way for the leading moderate candidate to make any headway against the hard-line presidential front-runner is to convince millions of Iranians to bother voting at all.

Former central bank chief Abdolnaser Hemmati is pitching himself as a reform-friendly centrist to revive Iran’s relations with the West and allow more personal freedoms, including a more prominent role for women. He is currently polling in the low single digits, with many Iranians saying they will skip the ballot in protest at the way the country is run.

But the 64-year-old technocrat said he might be able to build enough momentum to pull off a surprise if he can persuade enough people to vote, despite the hard-line establishment’s attempts to sideline moderate and reformist candidates from a run at the presidency.

“Despite what they claim, the group of people running against me in these elections, they don’t believe in good foreign relations,” Mr. Hemmati said in an interview at his campaign office. “They don’t believe in social freedom for the people.”

Mr. Hemmati is the only reform-minded candidate left in the five-person race, after the Guardian Council, Iran’s election watchdog, disqualified nearly everyone else, save for one other reformist who pulled out of the contest Wednesday. The disqualifications, including those of prominent centrists, have smoothed the path of the leading ultraconservative, Ebrahim Raisi.

Abdolnasser Hemmati, second right, and Ebrahim Raisi, right, leave the stage at the conclusion of the final presidential debate ahead of the election.

Abdolnasser Hemmati, second right, and Ebrahim Raisi, right, leave the stage at the conclusion of the final presidential debate ahead of the election.

Photo: Morteza Fakhri Nezhad/Associated Press

Mr. Raisi lost the last election against the incumbent President Hassan Rouhani in 2017. He was instead appointed the country’s chief justice, overseeing the imprisonment of hundreds of political activists, journalists and dual citizens, including Americans, and was singled out for sanctions by the Trump administration.

If Mr. Raisi wins power during a time of growing tension in the region, political analysts expect him to steer Iran toward Russia and China instead of following Mr. Rouhani’s path of trying to improve diplomatic and economic relations with the U.S. and Europe. His victory would also confirm the ascendancy of hard-liners and could complicate negotiations with the U.S. over a multinational nuclear deal, which the Biden administration aims to rejoin in part to secure a broader agreement limiting Tehran’s military objectives across the Middle East.

While Mr. Raisi doesn’t oppose the nuclear deal, he says the U.S. can’t be trusted, echoing the stance of Iran’s Supreme Leader Ali Khamenei.

“A president really has the opportunity to tactically shift the direction of the country,” said Aniseh Bassiri Tabrizi, senior research fellow and leader of the Middle East program at the London-based Royal United Services Institute. “If the country moves further away from the West, toward Russia and China, that is going to be a very big shift.”

Abdolnasser Hemmati’s challenge is to mobilize voters who plan to stay at home and cast their votes for him.

Abdolnasser Hemmati’s challenge is to mobilize voters who plan to stay at home and cast their votes for him.

Photo: Maryam Rahmanian for The Wall Street Journal

Iran’s political factions are roughly divided into two main camps: right-wing hard-liners and liberal reformists. Moderate pragmatists, such as the current president, Mr. Rouhani, attempt to hold the middle ground.

Mr. Raisi currently leads the field by a wide margin. A poll released Monday by the Iranian Students Polling Agency projected him winning 61% of the vote, with support for Mr. Hemmati pegged at 3.7%. If Mr. Raisi fails to win more than half the vote on Friday, there will be a second-round runoff to determine the winner.

Mr. Hemmati’s challenge is to mobilize voters who plan to stay at home on and cast their votes for him.

Mr. Rouhani’s initial path to power back in 2013 gives him reason for optimism. One week before the election that year, Mr. Rouhani, who has now hit his two-term limit, was also polling in single digits. He later won a landslide victory with over 50% of the vote by appealing to the middle ground.

Mr. Hemmati’s prospects don’t look good at the moment. Millions of Iranians appear likely to boycott the vote after previous reformist and centrist leaders failed to satisfy the economic and social aspirations of a young population. Many Iranians see refusing to vote as a way of protesting against the system as a whole.

However, on Wednesday, Mr. Hemmati received a major boost of support when former president Mohammad Khatami, who remains a leading reformist figure, gave him his tacit endorsement when he praised the other nonconservative candidate Mohsen Mehralizadeh for bowing out of the race so as to not split the nonconservative vote. Mr. Khatami’s statement was also a sign that he did not call for a boycott of the vote. 

 Days earlier, on Monday, the Reformist Front, an umbrella group for most reformist parties in Iran, had voted to not endorse Mr. Hemmati, making it harder for him to persuade voters to provide their support.

Another leading reformist figure, Mir-Hossein Mousavi, who has been under house arrest for a decade for his role in the 2009 Green Movement protests, said in a public message that he stood with those who are fed up with what he called “engineered and humiliating elections,” indicating that he is also supporting a boycott.

“I can’t imagine it will become worse than this—economically, politically, socially,” said Tahmineh Kaveh, a 50-year-old state employee in Tehran who said she wouldn’t bother to vote on Friday. “It is the system that should change. It doesn’t matter if you replace one sprocket with another,” she said.

A poll released by the Iranian Students Polling Agency projected Ebrahim Raisi will win 61% of the vote.

A poll released by the Iranian Students Polling Agency projected Ebrahim Raisi will win 61% of the vote.

Photo: Maryam Rahmanian for The Wall Street Journal

Mr. Hemmati has attempted to draw a contrast with his hard-line presidential opponents. He supports boosting Iran’s international diplomacy with both regional rivals and Western countries. To underscore that agenda, Mr. Hemmati said he would invite the current, and relatively popular, foreign minister Javad Zarif to join his cabinet.

He blames Iran’s economic problems on U.S. sanctions, which under his watch over the central bank caused the national currency to lose up to 80% of its value, and inflation last year to hit 36%. His supporters say having a president with economic insight at a time of deep economic crisis would make a difference.

“He really prevented the economy from collapsing,” said Mikaeel Mohammadi, a 30-year-old engineer who planned to vote for the former banker.

Mr. Hemmati also says Iran needs a more open society and his candidacy has resonated with some of Iran’s liberals. Mehdi Karroubi, another Green Movement leader under house arrest, has encouraged Iranians to vote for Mr. Hemmati, who appears to be eager to target women voters in particular.

During his campaign, Mr. Hemmati appointed his wife to represent him in a television interview—an unusual move in Iranian politics. Rather than a more conservative full-body cloak that has been the norm for Iranian first ladies, who rarely appear in public, Sepideh Shabestari appeared before the cameras wearing a colorful head scarf. She has also registered a Twitter account to mobilize female voters.

Supporters of Ebrahim Raisi during an election campaign rally in Tehran on Monday.

Supporters of Ebrahim Raisi during an election campaign rally in Tehran on Monday.

Photo: Maryam Rahmanian for The Wall Street Journal

Mr. Hemmati says he thinks Iran’s wavering voters will ultimately decide to take part in the election. “I believe that at the last minute, when they are worried [about a hard-liner winning], they will vote,” Mr. Hemmati said.

Still, the momentum that carried Mr. Rouhani into office in the years following the mass protests of 2009 appears lacking today, said Abbas Abdi, a prominent reformist analyst in Tehran. In 2013, Mr. Abdi said, “there was a car ready to get started and drive. And Mr. Rouhani had the potential and capability to go with it.”

“Today, there is no car,” he said. “There is not even gasoline.”

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Write to Sune Engel Rasmussen at sune.rasmussen@wsj.com