But his right-wing political movement earned just under half of votes cast in the April 8 poll.
That means there is an 18% gap between the proportion of votes won and the share of parliamentary seats given.
Lithuania came second in our study, while Poland, Greece and Latvia also had gaps of more than 10%.
The Netherlands, Germany, Denmark and Malta had the closest alignment in the bloc between share of votes and seats.
Most of the EU uses proportional representation (PR), which awards seats according to what proportion of the vote each party won.
Each country’s fairness of election was measured by looking at the deviation from proportionality.
France and the UK use variations of the first-past-the-post system (FPTP), with the former doing it over two rounds if no-one gets a majority first time around.
The two countries at the top of our analysis — Hungary and Lithuania — both have a mixture of PR and FPTP
Orban and his Fidesz party introduced this hybrid system after reform ahead of Hungary’s previous election in 2014.
The changes included reducing the number of parliamentary seats from 386 to 199, which experts say has widened the gap between the ruling party and the opposition.
It comes after tens of thousands of Hungarians protested in Budapest at the weekend over Orban’s election victory.
They are upset his campaign allegedly concentrated too much on “hate” and say the electoral system in Hungary is unfair.
In their Facebook post, the rally’s organisers said: “Fidesz’s election system and the government’s hate campaign have pushed the majority into a one-third (parliamentary) minority.”
In the election campaign Orban projected himself as the defender of Hungary’s Christian culture against Muslim migration into Europe, an image which resonated with millions of voters, especially in rural areas.
But the opposition’s poor showing was at least partly of its own making as rival candidates split the anti-government vote in five districts in Budapest, where preliminary results showed a slim Fidesz victory.
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