Both he and another man are wanted for attempted murder for a Novichok attack on Sergei Skripal and his daughter Yulia in March.
At a news conference in the Houses of Parliament on Tuesday, Bellingcat investigator Cristo Grozev said Mr Mishkin - like Mr Chepiga - was a member of the GRU and given the celebrated award in the autumn of 2014 for "actions in Ukraine".
Bellingcat's findings also cast doubt on Russia's claims that Boshirov and Petrov were civilians and that the government had no knowledge of the Skripal attack.
"We have now identified "Alexander Petrov" to be in fact Dr. Alexander Yevgenyevich Mishkin, a trained military doctor in the employ of the GRU", the British-based group said in a report published on its website.
The website says: "During his medical studies, Mishkin was recruited by the GRU, and by 2010 had relocated to Moscow, where he received his undercover identity - including a second national ID and travel passport - under the alias Alexander Petrov".
The Skripals were found unconscious on March 4 on a bench in the southern English town of Salisbury.
Following the attack in March, a United Kingdom investigation blamed Russian Federation for the poisoning which they've always denied.
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Footage released by London police of the two suspects in the poisoning of Sergei Skripal. But the nerve agent killed a British woman, Dawn Sturgess, and seriously sickened her partner.
He studied and graduated from a military medical academy in Russia and then trained as a doctor for the Russian armed naval forces.
The website said it discovered Mishkin's real identity after obtaining a scanned copy of his passport.
Ruslan Boshirov and Alexander Petrov give an interview to the RT news channel.
Both suspects have appeared on Russian TV to deny any link to the Salisbury poisonings.
They explained that they went to the small town as tourists and had always wanted to see its tower.
The US Justice Department also charged seven GRU officers in an alleged worldwide hacking rampage that targeted more than 250 athletes, a Pennsylvania-based nuclear energy company, a Swiss chemical laboratory and the chemical weapons watchdog.