Hungarian Prime Minister Viktor Orban's Fidesz party has lost the two-thirds supermajority it held in parliament since 2010, which allowed it to pass a new constitution and other legislation without input from the opposition.

The National Election Office said Sunday that Zoltan Kesz, an independent supported by the left-wing opposition parties, defeated Fidesz candidate Lajos Nemedi in a district centered on the city of Veszprem by 42 percent to 37 percent.

The election was needed because Fidesz's Tibor Navracsics, who won the seat in April, has since become a European Union commissioner.

Orban's Fidesz party and a much smaller ally have also used their supermajority in the 199-seat legislature to dominate institutions including the state media authority and the constitutional court by electing only government-backed nominees.