Navalny, who crusaded against official corruption and staged massive anti-Kremlin protests as President Vladimir Putin's fiercest foe, died in the Arctic penal colony in February 2024. He was serving a 19-year sentence that he believed to be politically motivated.
Authorities said that the politician became ill after a walk but have otherwise given few details on his death. He was 47.
In a video released Wednesday, Yulia Navalnaya said that biological samples from Navalny's body had been taken out of Russia and tested at two laboratories abroad.
She said that both laboratories concluded that Navalny had been poisoned, but had not released their findings due to "political considerations." She did not elaborate on what the alleged poison was.
"These labs in two different countries reached the same conclusion: Alexei was killed. More specifically, he was poisoned," Navalnaya said in the video, which was posted on social media.
"I demand that the laboratories that conducted the research publish their results," she said. "Stop appeasing Putin for some higher 'considerations.' You cannot placate him. While you stay silent, he does not stop."
Navalnaya has repeatedly blamed Putin for Navalny's death, something which Russian officials have vehemently denied. The Kremlin has not yet commented on Navalnaya's latest statement.
Navalnaya said in August 2024 that she was told by Russian investigators that Navalny died from a combination of "a dozen different diseases" and that he finally succumbed to arrhythmia, or an irregular heartbeat.
Navalnaya disputed Russian officials' version of events and said her husband exhibited no instances of heart disease while alive.
Navalny previously suffered from another poisoning in 2020, when the opposition leader fell sick on an internal flight in Russia. He was flown to Berlin while still in a coma for treatment two days later. Labs in Germany, France and Sweden, and tests by the Organization for the Prohibition of Chemical Weapons, established that he was exposed to the Soviet-era Novichok nerve agent.
Russian authorities have denied any involvement in the incident, a claim that Navalny challenged as false.