Sergei Skripal and his daughter Yulia Skripal became critically ill after being exposed to a nerve agent in March.
He is also known as Alexander Petrov, but was fully unmasked recently.
Russian Federation has always denied the allegations and claims the suspects are "ordinary civilians".
Mishkin, 39, trained as a military doctor in Russia's intelligence agency GRU.
He was recruited by GRU during his studies at one of Russia's military medical academies, and between 2011 and 2018 he traveled repeatedly under the identity of Alexander Petrov, including to Ukraine and Moldova's breakaway territory of Transdniestria.
The second of two Russians, who Britain says was responsible for the poisoning of former Russian spy Sergei Skripal and his daughter, is named by investigative website Bellingcat as a military doctor for Russia's GRU military intelligence.
British Prime Minister Theresa May said the attack was likely ordered at the highest levels of the Russian government, an allegation vehemently rejected by Russian President Vladimir Putin.
The second man believed to be behind a nerve agent attack in Salisbury, England, has been identified as a Russian military doctor.
A woman later died from Novichok poisoning after her partner found a counterfeit perfume bottle which police believe had been used to smuggle the nerve agent into Britain.
Last week, authorities in the Netherlands alleged the GRU tried and failed into the world's chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons.
Bellingcat says it "conclusively identified" Mishkin from "multiple open sources, testimony from people familiar with the person, as well as copies of personally identifying documents", including his passport.
Both suspects have appeared on Russian TV to deny any link to the Salisbury poisonings.
The prosecutors said at the time the two were undercover GRU officers.