The British open-source website said it had identified the suspect using testimonies from people the suspect knew and a scanned copy of his passport.
Last month, Bellingcat named the first suspect in the poisoning scandal as Anatoliy Chepiga.
"While Aleksandr Mishkin'strue persona has an even sparser digital footprint than Anatoly Chepiga's, Bellingcat has been able to establish certain key facts from his background", the October 8 report said.
"In the period 2011-2018, Alexander Mishkin travelled extensively under his new identity".
Following the attempted poisoning, United Kingdom investigators said one of the two suspects had travelling under the name Ruslan Boshirov.
Unlike Chepiga, awarded the Hero of the Russian Federation award by Putin in 2014, Mishkin appears to have either been less deeply undercover or sloppier - his "cover identity retained most of the biographical characteristics of the authentic Mishkin - such as the exact birth date, first and patronymic name, and first names of his parents", Bellingcat said, and until 2014, his Moscow home address was the same as GRU headquarters.
Sergei Skripal, a former colonel in Russia's GRU military intelligence service, and his 33-year-old daughter Yulia were poisoned in March by a liquid form of Novichok, a substance originally developed in the former Soviet Union. Sergei Skripal and his daughter Yulia both survived the attack but a woman who later found the poison, which had been hidden in a perfume bottle, wasn't so lucky.
The poisoning of Skripal, a former Russian agent who was convicted of spying for Britain, became a major worldwide incident.
He studied and graduated from a military medical academy in Russia and then trained as a doctor for the Russian armed naval forces.
The US Justice Department also charged seven GRU officers in an alleged global hacking rampage that targeted more than 250 athletes, a Pennsylvania-based nuclear energy company, a Swiss chemical laboratory and the chemical weapons watchdog.
The home of former Russian spy Sergei Skripal on Christie Miller Rd in Salisbury, Wiltshire under police guard.
In reaction to Bellingcat's latest report, British police said they would not comment on speculation regarding the real identities of those charged with poisoning the Skripals.