Wagner Group commander Dmitry Utkin was on the plane with Yevgeny Prigozhin that crashed north of Moscow, the Russian civil aviation authority has said.
There were no survivors after the jet crashed near the village of Kuzhenkino Tver region, north of Moscow, according to Russian authorities.
Civil aviation authority Rosaviatsia published the names of seven passengers, including Wagner boss Prigozhin and Utkin, along with three crew members it said had been on board.
Eight bodies have been recovered from the wreckage so far, authorities said.
Utkin - a former Russian soldier reportedly adorned with Nazi tattoos - has been described as Prigozhin's right-hand man and allegedly played a key role in the founding of the Wagner Group.
Previously, Utkin was a lieutenant colonel in the GRU military intelligence service and was deployed twice to Chechnya.
The 53-year-old has also been accused of involvement in numerous war crimes, including in Homs, Syria, where he reportedly gave the order to beat a deserter to death and demanded the act be filmed.
Video footage appears to show the moment of the plane crash.
In the clip, the aircraft is seen plummeting to the ground, followed by a trail of smoke - before it smashes into a field.
The plane was heading from Moscow to St Petersburg.
Prigozhin led a short-lived mutiny against Russia's top military brass in June, and was described at the time by Vladimir Putin as a "traitor".
The Russian mercenaries surged most of the way to Moscow before Prigozhin called off the advance and ordered them to turn back to "avoid bloodshed".
The Kremlin said his fighters would either retire, follow him there, or join the Russian military.
In the aftermath, Andrei Gurulev, a retired general and politician, said Prigozhin and Utkin deserved "a bullet in the head" for their role in the attempted rebellion.
"I firmly believe that traitors in wartime must be executed," he added.