DUBAI, United Arab Emirates — Reformist candidate Masoud Pezeshkian won Iran’s runoff presidential election Saturday, besting hard-liner Saeed Jalili by promising to reach out to the West and ease enforcement on the country’s mandatory headscarf law after years of sanctions and protests squeezing the Islamic Republic.

Mr. Pezeshkian promised no radical changes to Iran’s Shiite theocracy in his campaign and long has held the country’s supreme leader, Ayatollah Ali Khamenei, as the final arbiter of all matters of state in the country. 

Even Mr. Pezeshkian’s modest aims, though, will be challenged by an Iranian government still largely held by hard-liners, the ongoing Israel-Hamas war in the Gaza Strip, and Western fears over Tehran enriching uranium to near-weapons-grade levels.

A vote count offered by authorities put Mr. Pezeshkian as the winner with 16.3 million votes to Mr. Jalili’s 13.5 million in Friday’s election. 

Overall, Iran’s Interior Ministry said 30 million people voted in an election held without internationally recognized monitors.

Supporters of Mr. Pezeshkian, a heart surgeon and longtime lawmaker, entered the streets of Tehran and other cities before dawn to celebrate as his lead grew over Mr. Jalili, a hard-line former nuclear negotiator.

“Dear people of Iran, the elections are over and this is just the beginning of our cooperation,” Mr. Pezeshkian wrote on the social platform X, still banned in Iran. 

He added that “the difficult path ahead will not be smooth except with your companionship, empathy and trust. I extend my hand to you and I swear on my honor that I will not leave you alone on this path. Do not leave me alone.”

Mr. Pezeshkian’s win still sees Iran at a delicate moment, with tensions high in the Mideast over the Israel-Hamas war, Iran’s advancing nuclear program, and a looming American election that could put any chance of a detente between Tehran and Washington at risk. 

Mr. Pezeshkian’s victory also wasn’t a rout ofMr.  Jalili, meaning he’ll have to carefully navigate Iran’s internal politics as the doctor has never held a sensitive, high-level security post.

The first round of voting on June 28 saw the lowest turnout in the history of the Islamic Republic since the 1979 Islamic Revolution. Iranian officials have long pointed to turnout as a sign of support for the country’s Shiite theocracy, which has been under strain after years of sanctions crushing Iran’s economy, mass demonstrations and intense crackdowns on all dissent.

Government officials up to Ayatollah Khameni predicted higher turnout as voting got underway, with state television airing images of modest lines at some polling centers. 

However, online videos purported to show some polls empty while a survey of several dozen sites in Tehran saw light traffic and a heavy security presence on the streets.

Authorities put turnout in Friday’s vote at 49.6 percent, still historically low for an Iranian presidential election. They counted 607,575 voided votes — which often are a sign of protest by those who feel obligated to cast a ballot but reject both candidates.

Mr. Pezeshkian, who speaks Azeri, Farsi and Kurdish, campaigned on outreach to Iran’s many ethnicities. He represents the first president from western Iran in decades — something people hope will aid the county as those in the western part are considered more tolerant because of the ethnic and religious diversity in their area.

The election came amid heightened regional tensions. In April, Iran launched its first-ever direct attack on Israel over the war in Gaza, while militia groups armed by Tehran — such as the Lebanese Hezbollah and Yemen’s Houthi rebels — are engaged in the fighting and have escalated their attacks.

Iran is also enriching uranium at near weapons-grade levels and maintains a stockpile large enough to build several nuclear weapons, should it choose to do so. 

And while Ayatollah Khamenei remains the final decision-maker on matters of state, whichever man ends up winning the presidency could bend the country’s foreign policy toward either confrontation or collaboration with the West.

Crown Prince Mohammed bin Salman of Saudi Arabia, which has reached a detente with Iran, sent his congratulations to Mr. Pezeshkian that stressed his “keenness to develop and deepen the relations that bring our two countries and peoples together.” 

President Putin, who has relied on Iranian-made drones in his war on Ukraine, similarly congratulated Pezeshkian.

There was no immediate response from America.

The campaign also repeatedly touched on what would happen if President Trump, who unilaterally withdrew America from the Iran nuclear deal in 2018, won the November election. 

Iran has held indirect talks with President Biden’s administration, though there’s been no clear movement back toward constraining Tehran’s nuclear program for the lifting of economic sanctions.

Though identifying with reformists and relative moderates within Iran’s theocracy during the campaign, Mr. Pezeshkian at the same time honored Iran’s paramilitary Revolutionary Guard, on one occasion wearing its uniform to parliament. 

He repeatedly criticized America and praised the Guard for shooting down an American drone in 2019, saying it “delivered a strong punch in the mouth of the Americans and proved to them that our country will not surrender.”

More than 61 million Iranians over the age of 18 were eligible to vote, with about 18 million of them between 18 and 30. Voting was to end at 6 p.m. but was extended until midnight to boost participation.

The late president, Ebrahim Raisi, who died in a May helicopter crash, was seen as a protégé of Ayatollah Khamenei and a potential successor as supreme leader.

Still, many knew him for his involvement in the mass executions that Iran conducted in 1988, and for his role in the bloody crackdowns on dissent that followed protests over the 2022 death of Mahsa Amini, a young woman detained by police over allegedly improperly wearing the mandatory headscarf, or hijab.