Aleksei A. Navalny, an anticorruption activist who for more than a decade led the political opposition in President Vladimir V. Putin’s Russia while enduring arrests, assaults and a near-fatal poisoning, died on Friday in a Russian prison. He was 47.

His death was announced by Russia’s Federal Penitentiary Service and a spokeswoman for Mr. Navalny.

The spokeswoman, Kira Yarmysh, said on Saturday in a statement on X that Mr. Navalny’s mother had been officially notified of his death. Ms. Yarmysh said Russian investigators had transferred Mr. Navalny’s body from the penal colony in the Arctic where he has been held to a nearby town for examination. No cause of death has been specified.

Mr. Navalny had been serving multiple sentences that would most likely have kept him in prison until at least 2031 on charges that his supporters say were largely fabricated in an effort to muzzle him. Despite increasingly harsh conditions, including repeated stints in solitary confinement, he maintained a presence on social media, while members of his team continued to publish investigations into Russia’s corrupt elite from exile.

Mr. Navalny was given a three-and-a-half-year prison sentence in February 2021 after returning to Russia from Germany, where he had been recovering from being poisoned the previous August. In March 2022, he received a nine-year sentence for embezzlement and fraud in a trial that international observers denounced as “politically motivated” and a “sham.” And in August 2023, he was sentenced to 19 years in prison for “extremism.”