The result means that Tisza looks set to receive a supermajority in parliament.
"We did it. Together we have brought down the Orbán regime," Péter Magyar told cheering supporters in the capital, Budapest, according to AFP.
A few hours earlier, Viktor Orbán had phoned to congratulate the victors and admitted defeat after the forecast showed an overwhelming victory for Tisza.
"I congratulate the victorious party. We will serve the Hungarian nation and our homeland in opposition," Orbán said in a speech in Budapest.
The reaction from the EU came just minutes after the election results were announced earlier on Sunday evening:
"The heart of Europe beats stronger in Hungary today," wrote European Commission President Ursula von der Leyen in both Hungarian and English on social media after the announcement.
16-year rule ends
The announcement of Tisza's election victory came shortly after 9 p.m., when 53 percent of the votes had been counted.
Later, with over 93 percent of the votes counted, Tisza had won 138 of the 199 seats in parliament. Orbán's Fidesz party, together with the coalition party KDNP, had only a total of 54 seats.
The 16-year rule of the EU-critical Viktor Orbán is thus over.
In addition, the landslide victory looks set to give the more EU-friendly Tisza a so-called supermajority - a two-thirds majority in parliament - which could open the way for constitutional amendments, for example.
The far-right party Mi Hazánk is expected to win 7 seats, according to the forecast, which would mean that parliament will have a strong tilt towards center-right parties.
Record high participation
Polls closed at 7 p.m. on Sunday with a record-high voter turnout. By 6:30 p.m., a preliminary 77.8 percent of Hungarians had cast their ballots, according to the election authority.
This can be compared to the elections in 2022 and 2018, when the corresponding figure at the same time was around 68 percent, according to the Europe Elects platform.
The previous record was set in the 2002 election and was 70.5 percent.
Facts: Parliamentary elections in Hungary
Each voter has two votes: one for their own constituency and one for national party lists.
Of the 199 seats in the Parliament (Országház), 106 are elected via constituencies. 93 seats are distributed proportionally based on national party lists.
The electoral system also has a peculiarity, sometimes called winner's bonus, which is considered to favor large parties. This means that the votes that the winner in a constituency receives in addition to what was required to win are added to the party in the national count.
The result is that a large party can receive more seats than its vote share would suggest. The system is considered to have contributed to Viktor Orbán's government party Fidesz gaining a two-thirds majority in recent elections despite a vote share of around 45-50 percent.
Special rules also apply to make it easier for 13 specific national minorities (of which Roma, Germans and Slovaks are the most numerous) to win individual mandates.
Parliament has a 5 percent threshold.
Hungary has just over 7.5 million eligible voters.
Sources: UI, NE.
Fidesz: Nationalist right-wing party. Led by Prime Minister Viktor Orbán. Clearly critical of the EU, has close contacts with Moscow. Accused, among other things, of authoritarian rule. It is in alliance with the Christian Democratic Party of Hungary (KDNP).
Tisza: Social conservative right-wing party. Led by Péter Magyar, former member of Fidesz. The party is considered more pro-EU than Fidesz. Also called the Respect and Freedom Party.
Democratic Coalition (DK – Demokratikus Koalíció): Social democratic and social liberal party.
Our Homeland (MH - Mi Hazánk): An extreme right-wing party that is also described as neo-fascist.
Sources: Politico.org, Expo, UI.
