Orban, 50, has had repeated rows with the European Union and foreign investors, particularly over heavy taxes imposed on the country's mostly foreign-owned banks, telecoms and energy firms, and increased state control over the energy sector.
But he is popular with many voters for stabilising public finances and cutting their electricity and gas bills. Opinion polls show his Fidesz party is on course for a landslide victory.
"I would like to see high turnout because that would allow stronger governing," Orban told Reuters after he cast his vote early at a school in the capital.