Russia's civil aviation authority says Wagner group boss Yevgeny Prigozhin and Wagner commander Dmitry Utkin were on board a private jet that crashed in Russia's Tver region north of Moscow, with no survivors.
The pair, who were on the passenger list of the crashed jet, had previously attended a meeting with officials from the Russian Defence Ministry.
A Telegram channel linked to the Wagner Mercenary Group reported that Prigozhin had died.
"The head of the Wagner Group, a Hero of Russia, a true patriot of his Motherland, Yevgeny Viktorovich Prigozhin died as a result of the actions of traitors to Russia," a post in the Grey Zone channel said.
"But even in Hell, he will be the best! Glory to Russia!"
Eight bodies have been found and all 10 people aboard died in the crash.
The Embraer aircraft, en route from Moscow to St Petersburg, was carrying seven passengers and three crew.
The plane had been in the air less than 30 minutes when it crashed.
Russia's Federal Agency of Air Transport announced it had launched an investigation.
"An investigation has been launched into an Embraer plane crash that occurred tonight in the Tver region," its statement read.
"According to the passenger list, the name and surname of Yevgeny Prigozhin is among them."
"There were 10 people on board, including three crew members. According to preliminary information, all on board were killed," Russia's Ministry of Emergency Situations said in a statement.
The governor of the Tver region, Igor Rudenya, had assumed control of the situation with law enforcement on the scene, the agency reported.
A separate but routine criminal investigation was also launched by the Russian Investigative Committee due to the incident involving an aircraft.
Unconfirmed media reports said the jet belonged to Mr Prigozhin.
Flight tracking data reviewed by The Associated Press showed a private jet registered to Wagner that Mr Prigozhin had used previously took off from Moscow on Wednesday evening and its transponder signal disappeared minutes later.
Soon after the jet crashed, a second private jet linked to Mr Prigozhin that also appeared to be heading to St Petersburg turned back to Moscow and later landed, flight tracking data showed.
Mutiny may have left Prigozhin vulnerable
On Tuesday, Mr Prigozhin posted his first video message on social media since the mutiny that saw Russian President Vladimir Putin label him a traitor.
In it, he spoke about the work the Wagner group was doing in Africa.
"Justice and happiness for the African people. We're making life a nightmare for ISIS and Al Qaeda and other bandits," Mr Prigozhin said.
In July, CIA director William Burns told a security forum he thought Mr Prigozhin could be killed as retribution for the uprising.
"If I were Prigozhin, I wouldn't fire my food taster," he said.
Mr Prigozhin was the man behind June's mutiny in Russia, when his private army briefly took control of the regional centre Rostov-on-Don and began marching towards Moscow.
Some onlookers assessed the flashpoint as making Mr Putin look the most vulnerable he has since he came to power in Russia, a nation he has led for more than two decades.
Mr Putin would later accuse the "organisers of the rebellion" of "betraying their country".
While even peaceful protests in Russia can draw severe punishments from authorities, Mr Prigozhin and his Wagner mercenaries were, largely, left alone in the incident's aftermath.
Despite living in exile in Belarus post-uprising, Mr Prigozhin was seemingly able to travel to Russia and appeared at a meeting of African leaders in St Petersburg.
Earlier this month, Jenny Mathers, a senior lecturer in international politics at Aberystwyth University, said the light touch Mr Putin had used so far on Mr Prigozhin and his Wagner mercenaries was "extraordinary".
"Russians protesting the war have been arrested for even holding blank pieces of paper, so the Wagner group has been treated remarkably gently," she said.
Story By Riley Stuart in London, Paul Johnson and Jenny Cai
Stay tuned for the latest news on our radio stations