BUENOS AIRES—President Javier Milei scored a decisive political win Sunday, strengthening his position in Argentina’s Congress and securing a lifeline for his audacious free-market revolution backed by President Trump.

With nearly 92% of votes counted, Milei’s Freedom Advances party won almost 41% of the national vote, putting it on track to more than double its representation in Congress. That means his party and allies should secure at least one-third of the seats in both chambers—the critical threshold that allows Milei to preserve his veto power and defend his sweeping decrees.

The result, stronger than most polls had predicted, gives Milei fresh political momentum after months of unrest over deep spending cuts and a grinding recession last year. It also shores up his standing with Washington and the International Monetary Fund, which have tied future financial support to the survival of his austerity experiment. Market analysts expect Argentine bonds and the peso to rally when trading opens Monday, reflecting relief that Milei still has political traction.

The U.S. announced a $20 billion currency swap this month to prop up Argentina’s currency and promised to raise another $20 billion from private banks and sovereign-wealth funds.

Trump has made it clear his support was contingent on Milei’s electoral success. “If he wins, we’re staying with him. And if he doesn’t win, we’re gone,” Trump said this month.  

Milei swept to power two years ago on the promise of radical change, vowing to end the nation’s decadeslong struggle with runaway inflation and economic ruin through relentless spending cuts. The messy-haired libertarian economist promised “anarcho-capitalism” and often appears in public with a chain saw to demonstrate how he was aggressively cutting spending to drive change.

Milei sharply devalued the peso to unify an array of exchange rates and curb a chronic budget gap that was funded by printing money. He also reduced energy subsidies and fired tens of thousands of public-sector employees. The policies briefly stabilized Argentina’s finances, producing the first balanced budget in more than a decade. The country’s infamously high inflation rate has fallen to 32% from 200% two years ago.

The measures—part of what Milei calls shock therapy—have restored some credibility to Latin America’s third-largest economy, but about one in three people still live in poverty. He came into the election with polls showing his party could lose badly.

While many voters were ready to criticize the president, they said handing back power to the leftist Peronist opposition was unthinkable.

“Milei is putting the country back on its feet,” said Leandro Pedrozo, a 20-year-old law student, who said many of his friends and family had left Argentina during financial crises under Peronist governments. “I’m not leaving—I had the chance to go live in Europe, but no! I’ve decided to bet on my country.”

Milei’s party entered the vote with just 37 deputies and six senators, around 15% of Congress and 10% of the Senate, respectively. The midterm gains leave him still far from a majority but enough to give him effective veto power over hostile legislation. Analysts say holding one-third of either chamber is crucial for sustaining his presidential decrees and fending off attempts by the opposition to reverse his fiscal agenda.

“No one was expecting this impressive comeback,” said Rodrigo Zarazaga, a Jesuit priest who has worked as a chaplain for decades in the slums of the Buenos Aires province, home to half of the country’s poor and 40% of the country’s voters.

The Peronist opposition—which has dominated Argentine politics for most of the past 80 years—performed below expectations. The party, founded by Juan and Eva Perón in the 1940s and long associated with Argentina’s welfare state, remains a formidable force but failed to mobilize disenchanted voters as inflation eased from its historic highs.

Middle-class Argentines also voted against the Peronists to prevent a financial meltdown and social turmoil after the pivotal election.