He exited the gray jumbo jet to excited but muffled applause from several airport employees in neon vests. At least one companion approached him giddily for a selfie.

Nearly three months after fleeing Mozambique, saying he feared for his life, opposition leader Venâncio Mondlane returned Thursday to try to claim what he insists is rightfully his: the presidency.

Mozambique is scheduled to inaugurate a new president from the long-time ruling Frelimo party on Wednesday. Daniel Chapo of Freli won with 65 percent of the vote in the October election, according to the country’s highest court. According to the official tally, Mr. Mondlane won only 24 percent.

After several independent election observers identified irregularities in the voting, Mr. Mondlane spent months claiming the race was stolen, calling on his supporters to take to the streets. Some protests turned violent, with at least 250 people killed during a police response that rights groups called unnecessarily brutal.

The return of Mr. Mondlanea comes at a delicate time for this mineral- and gas-rich nation of 33 million. The government is struggling to solve the housing and debt crisis, and to quell a years-long insurgency backed by the Islamic State. Regional leaders such as South Africa have sent envoys to try to mediate a political impasse that has stalled trade and threatens further economic damage.

However, the outspoken opposition candidate refused to step down. “I, Venâncio Mondlane, elected president by the Mozambican people,” he said, raising his right hand in front of a crowd of news cameras outside the airport in the capital Maputo, “swear on my honor to serve Mozambique and Mozambicans.”

About a quarter of a mile away, thousands of his supporters crowded the police barricades, chanting, “The president has arrived! The president has arrived!” under the steady rain. The police used tear gas to keep the crowd at bay.

Filipe Nyusi, the incumbent president, brought the leaders of the main opposition parties together for a meeting on Thursday to discuss solutions – an exercise some say lacked credibility because Mr. Mondlane was not there. After the meeting, Mr. Chapo said the parties agreed to consider changes to the electoral law and the constitution “to adapt to the interests of Mozambicans”.

Fifty-year-old Mr. Mondlane might appear to some as a choice denier and populist troublemaker. But to his supporters, he is a singular figure at one point in time. Voters across southern Africa, led by a restive youth population, have rebuked former liberation parties at the polls over the past year.

Corruption, unemployment, inequality and poor living conditions have fueled widespread anger in Mozambique and across the region against political leaders seen as out of touch. Mr. Mondlane used that wave of discontent to offer a simple message: he would return the land to the people.

As celebratory crowds gathered at Mr. Mondlane’s motorcade in Maputo on Thursday, witnesses say police, with little provocation, responded with tear gas and bullets, leaving at least one man dead on the pavement with blood gushing from his head. A police spokesman declined to comment on any deaths, saying they were still gathering information.

“What people in Mozambique don’t want is Frelimo,” said Francisco Victor Chimene, a 25-year-old driver, standing next to an outdoor market where Mr. Mondlane had previously addressed a large number of his supporters. “What we want is change. We see that Venâncio will change this country.”

Educated in agronomy, Mr. Mondlane has a varied resume. He worked as a banker, a Pentecostal pastor and a television expert. His political breakthrough came in 2013 when he unsuccessfully ran for mayor of Maputo. He lost the mayoral race again two years ago, but the result was hotly contested with civil society organizations claiming massive fraud. The court ordered a recount in the main district due to irregularities.

After losing the leadership battle in Mozambique’s main opposition party, Renamo, Mr. Mondlane ran for president last year with the support of a smaller party, Podemos. His meteoric rise as a candidate attracted global attention, winning him support among right-wing populist figures abroad, even as young, left-leaning voters rallied behind him at home.

IN video posted on social networks during last year’s campaign, Mr Mondlane thanked Jair Bolsonaro, the former Brazilian president accused of plotting a coup, and called him “a man of God”.

Mr. Mondlane see Mr. Bolsonaro “as a pioneering man,” said Jonatas Feitosa, a pastor of a conservative evangelical church in Brazil and a friend of Mr. Mondlane. Mr. Bolsonaro presented himself as an antidote to the leftist party that has dominated Brazilian politics for more than a decade.

Frelimo, which has its roots in communism, has ruled Mozambique since the country’s independence from Portugal in 1975. But the party has since lost the trust of many Mozambicans due to widespread corruption. The government’s violent response to the post-election protests was seen by many as an indication of Frelimo’s desperate attempt to hang on to power.

During his presidential campaign, Mr. Mondlane traveled to Portugal, where he met with André Ventura, the president Chega, a far-right nationalist party which supports stricter immigration measures and has fought against the return of former colonies. But Chega has also fashioned himself as a champion of the working class, like Mr. Mondlane.

Mr. Ventura said in an email that his party hopes to build a common political platform with Mr. Mondlane, which is focused on “the fight against corruption and crime, the defense of family and order, and the resolution of the collapse of justice and other institutions.”

Mr. Mondlane has not spoken publicly about his ties to right-wing figures abroad. But in a country where most voters struggle to find their next meal or a stable home to live in, those ties don’t matter, said Benjamin Francisco Malate, a 38-year-old businessman.

“The reason we support Venância is not because he is from the left or the right,” said Mr. Malate. “We just support the solutions he presents.”

Some of his proposals include policies that would require significant government intervention, such as building three million homes in five years and funding businesses for youth and women.

While standing on top of a car surrounded by thousands of people in Maputo on Thursday, Mr. Mondlane said that if the government goes ahead with the inauguration next Wednesday, the country will have two presidents. “Who runs this country?” Mr. Mondlane shouted into the loudspeaker.

“It’s the people,” answered the crowd.

Ana Ionova contributed reporting from Rio de Janeiro and Tiago Carrasco from Lisbon.