Footage from the cramped Minsk court showed Bialiatski, who co-founded the Viasna (Spring) human rights group, looking sombre, his hands cuffed behind his back, as he and his co-defendants watched proceedings from a courtroom cage.
Bialiatski, who was arrested in 2021, and three co-defendants were charged with financing protests and smuggling money.
Belarusian state news agency Belta confirmed the court had handed down long jail sentences to all the men, including a decade in prison for Bialiatski.
That, she said, placed human rights defenders at risk of criminal prosecution for their legitimate activities.
Viasna, the organisation he co-founded, took a leading role in providing legal and financial assistance to those jailed.