After his stunning win last night, Peter Magyar told a rally that "Hungary wants to be a European country again".
But while he is now set to lead a majority government after ousting Viktor Orban, Mr Magyar was once a loyal ally of the outgoing prime minister.
The 45-year-old served as a foreign affairs official under Mr Orban's 2010 administration before resigning from the Fidesz party in 2024 over a scandal involving a presidential pardon for a man convicted of helping cover up a sex abuse scandal at a children's home.
Hungary election live - follow the latest
The centre-right Tisza Party emerged as the strongest opposition party in Hungary after the 2024 European Parliament elections.
Mr Magyar has pledged to crack down on corruption, unlock billions of euros in frozen European Union funds, and tax the wealthiest, while reforming Hungary's crumbling healthcare system.
Most independent polls leading up to election day put Mr Magyar ahead of Mr Orban, and preliminary election results project that Tisza won 136 seats in Hungary's 199-member parliament.
The election saw a record 77.8% turnout, the highest ever in a Hungarian election, according to the country's national election commission, which says the "election process was conducted lawfully and smoothly across the country".
Voters in Hungary were angered after three years of economic stagnation and soaring living costs, along with oligarchs close to the government earning greater wealth.
Mr Magyar ran a "positive campaign" on boosting the economy, restoring healthcare and lowering the cost of living, according to Moscow correspondent Ivor Bennett.
"All of these domestic issues really chimed with people's needs here. They were desperate for change and fed up with the Orban government," he said, adding that Mr Orban ran a campaign of fear.
'Real blow for Putin'
Bennett said EU leaders will also be delighted to see the back of Mr Orban, who he described as a "Russian Trojan horse acting in Moscow's interest".
"He would consistently try to block aid to Ukraine, try to derail and slow down sanctions on Russia", he said.
"So for Vladimir Putin, a real blow. But for Europe, for Brussels, this is a moment to celebrate. Because that persistent thorn in their side has finally been removed after 16 long, long years."
Mr Magyar said during the election campaign that voters had to choose between "East and West", warning that Putin ally Mr Orban and his confrontational stance towards Brussels would take the country further away from the European mainstream.
With Mr Magyar in charge, many European leaders will now be hoping for an end to Hungary's adversarial role inside the EU, possibly paving the way for a £78.4bn (€90bn) loan to war-battered Ukraine, which was previously blocked by Mr Orban.
In his first remarks after the election, Mr Magyar promised his government would work for a free, European and humane Hungary after years of claims of corruption and shrinking freedoms.
He thanked those who voted for him and added: "As prime minister, I will work every day and every hour of the day for our country's security and development, as well as for the wellbeing of the Hungarian people."
Sex tape blackmail threat
In February, Mr Magyar accused the Fidesz Party of "Russian-type" blackmail, using a secretly-recorded sex tape showing consensual relations between him and a now ex-girlfriend at a party nearly two years ago.
"Even in Europe, it is unprecedented for a ruling party to attempt to discredit, blackmail and neutralise its main political opponent by secretly recording their sexual acts using illegal methods and threatening to make the recordings public," he wrote on X.
In an accompanying video, he said: "Of course, I don't know how the images and audio recordings illegally recorded in the apartment with secret service equipment will be manipulated afterwards."
He said there were what appeared to be drugs at the party, but denied taking any and offered to do a drug test.
Read more from Sky News:
Trump shares AI image of himself as Jesus
Britney Spears checks into rehab after DUI arrest
Mr Magyar said a photo of the bedroom the footage was filmed in with the caption "coming soon" was sent to Hungarian media. The photo was also published with the words "once upon a time..." on a website apparently named after Mark Radnai, the vice president of Tisza, who denied any involvement.
Tisza said in a statement it stands by Mr Magyar and that it "will not assist in manipulating politics with secretly recorded materials and threats".
(c) Sky News 2026: Who is Peter Magyar, Hungary's next prime minister?

Donald Trump shares AI image of himself as Jesus Christ after attacks on Pope Leo
Judge dismisses Trump's $10bn lawsuit against Wall Street Journal and Murdoch over reporting on Epstein ties
Fraudster who sold fake Oasis tickets given community order
Former Arsenal footballer Thomas Partey pleads not guilty to two further charges of rape