Fidesz is expected to win between 45 and 50% of the vote, polls suggest.
The centre-left opposition is facing a close race for second place with the far-right Jobbik party.
The Hungarian left has never fully recovered from its heavy defeat in the 2010 ballot, in which Viktor Orban swept to power with a two-thirds majority.
The election is mainly being fought over the state of the economy, correspondents say.
Socialist leader Attila Mesterhazy, who heads an opposition coalition of five parties, said he could still defeat Viktor Orban, despite trailing behind in opinion polls with around 25%.
“I don’t care about the polls, people are afraid of expressing their views,” Attila Mesterhazy said Saturday at a small rally in the capital, Budapest.
“I believe I will be prime minister.”
Critics say the state of democracy in Hungary has been eroded under Viktor Orban’s premiership.
The opposition – composed of five leftist and centrist parties – also accuses Viktor Orban of curtailing civil liberties and harming free speech.
But Fidesz has insisted that reform was needed in order to complete the work of eradicating the legacy of Communism from the country, and reduce the budget deficit to below the EU’s required 3% of gross domestic product.
Viktor Orban’s populist and Eurosceptic approach has proven popular with many Hungarians.
“The left had eight years to show what they can do, and they showed us all right,” Viktor Orban told Hungarian media on Saturday.
“Why on Earth should we believe that the same people and the same parties would not do the same if given another opportunity?”
Jobbik is also expected to do well in Sunday’s election, potentially receiving up to 20% of the vote.
Observers say the far-right party’s adoption of a softer image has paid dividends, as a recent opinion poll found leader Gabor Vona to be the most popular opposition politician.
sjnhHYqIbbMThree Indian nationals have been arrested and charged over the killing of Sikh separatist leader…
President Joe Biden has urged pro-Palestinian protesters on university campuses to uphold the rule of…
Blue Ivy Carter has joined the voice cast of The Lion King prequel Mufasa: The…
At least five people, including a four-month-old baby, have been killed after dozens of tornadoes…
Harvey Weinstein has been hospitalized just days after his 2020 rape conviction in New York…
Hamas has published a video showing the first proof of life of US and Israeli…