In the election, which international observers consider neither free nor fair, all 450 seats in the Duma, the lower house of parliament, are being elected.
Any opposition that questions Vladimir Putin or the full-scale Russian invasion of Ukraine has been barred from participating.
United Russia's 49.4 percent in the exit poll is in line with the 2021 election results. In the same poll, the Communist Party and the nationalist LDPR received 14.2 and 10.7 percent, respectively.
Voter turnout was around 55 percent on Sunday evening, according to the state news agency Tass, which is higher than in 2021 and 2016.
Russian citizens in occupied parts of Ukraine have been allowed to vote this year.
The head of the Russian election commission, Ella Pamfilova, said earlier on Sunday that more than 1,000 cyberattacks had been carried out against the election infrastructure. The attacks are so-called DDoS attacks, where the system is overloaded.
The attacks have been carried out by highly professional, well-coordinated groups that have used AI tools, Pamfilova said, according to state-controlled Russian media.
The election began last Friday and ends on Sunday.
