Orban was officially requested to form a new government by HungarianPresidentJanosAderMonday, and will be re-elected to the post in the first session of the new parliament Tuesday.
Meanwhile several hundred anti-government protesters formed a human chain around parliament in a symbolic protest late Monday.
Another anti-Orban demonstration expected to draw tens of thousands will also take place outside parliament on Tuesday evening.
They are part of a grassroots civil protest movement that has sprung up since April's parliamentary election, with opposition party leaders still reeling from the results.
Orban's ruling right-wing Fidesz party defied predictions of a tight contest by winning with a landslide 49 percent of the vote compared to under 20 for its nearest challenger, the nationalist Jobbik party.
That helped Fidesz clinch a third consecutive two-thirds parliamentary majority in a row, granting Orban further legislative carte blanche to amend the constitution and fast-track new laws.
Since the vote Orban has pledged to govern in the interests of all Hungarians, but has also called his triumph "the biggest mandate" since the switch from communism in 1990.
His election campaign was dominated by strident anti-immigration rhetoric, and early measures signalled by the government indicate he will continue in the same vein.
One of his first steps is likely to be the insertion of a constitutional clause preventing the "settlement of alien population".
Another package of bills targets non-governmental organisations funded by Hungarian-born US billionaire George Soros who Orban says orchestrates immigration.
Orban's critics meanwhile accuse him of removing democratic checks and balances and steering the country away from the European mainstream.
Further inroads on judicial and media independence, squeezed in recent years, are seen as likely by analysts.
'Corrupt system'
Since the election, two protests organised via social media by a group called "We are the Majority" have drawn tens of thousands in Budapest with smaller demonstrations taking place in cities around the country.
The protesters have formed a cross-section of society, spanning age, class and political affiliation, with rainbow and EU flags flown alongside ultra-nationalist symbols.
On the Facebook page for Tuesday's protest, organisers wrote: "We cannot let Orban's corrupt system deprive us of our freedom,...and our country's place in Europe".
Their demands include reform of the electoral system, redesigned by Fidesz in 2011 and which critics say helped deliver Orban's party its two-thirds majority, even though it won under half of the vote.
"This two-thirds wasn't even a half of the electorate, we don't consider this government legitimate," a protestor Katalin Kazmer, 71, told AFP Monday.
The protestors also want state media to adhere to non-partisan guidelines after international observers found "media bias" had helped tilt the poll in Fidesz's favour.
However, although opposition politicians also complained of widespread election-day irregularities, a poll last week said voters mostly blamed the bitterly divided parties themselves for their crushing defeat.
Their failure to forge an effective anti-Orban front has prompted calls that they should boycott the new parliament or even that a new opposition be built from scratch.
Although "personnel, policy, and moral renewal" of the opposition parties is a must, Daniel Hegedus, an analyst, told AFP the opposition parties better serve frustrated voters by staying in parliament.
"Coordinated parliamentary and street opposition will have to be built up together during the coming years," he said.
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