According to official figures, around two-thirds of Belarusians voted in favor of the constitutional amendment proposed by Head of State Alexandr Lukashenko.
"65.16 percent of voters voted for changes to the constitution of the Republic of Belarus," said the chairman of the Belarusian Central Election Commission, Igor Karpenko, according to Russian news agencies on Monday night.
Voter turnout was 78.63 percent.
The constitutional amendment allows Alexandr Lukashenko, who has been in power since 1994, to have further terms of office.
It also ties the former Soviet republic closely to Russia.
It provides for lifelong immunity for ex-presidents and a two-term limit on the term of office - but this is only to come into force with the next presidential election.
This means that the 67-year-old Lukashenko could stand for two more elections and remain in power until 2035 if he wins the elections.
repression and arrests
The opposition around Svetlana Tichanovskaya, who lives in exile, had declared the vote illegal because of the state's persecution of Lukashenko's critics.
According to human rights activists, hundreds of people were arrested in the run-up to the referendum on changing the constitution.
The human rights group Wesna listed the names of more than 300 people arrested on Sunday evening.
The videos published by the human rights activists show how people were taken away by police officers and larger groups demonstrated.
Putin and Lukashenko
In amending the constitution, Lukashenko is following the lead of Russian President Vladimir Putin, who held a referendum in 2020 that allowed him to remain in power until 2036.
The ruler in Minsk was able to count on Putin's help in crushing the mass protests after Lukashenko's controversial re-election in August 2020.
He used Belarus as a deployment area for his armed forces, which also attacked Ukraine from there on Thursday.
According to Lukashenko's wishes, the constitution of Belarus should also be changed so that Russian troops and nuclear weapons can be stationed permanently in the country in the future.