Nikolai Glushkov, 68, was discovered by his daughter late on Monday night at his suburban home in New Malden and his body was taken away in a private ambulance 24 hours later.
The Metropolitan Police said there was no evidence to suggest a link between the poisoning and Glushkovs death.
Scotland Yard has stated the unusual step of putting counter-terrorism officers in charge of the investigation is down to Glushkov's past.
London's Metropolitan Police force said counter-terrorism detectives were leading the investigation, "as a precaution because of associations that the man is believed to have had".
The Met said on Tuesday the next of kin had been informed.
"A postmortem examination will be held in due course".
Still, the poisoning and now the unexplained death have resurfaced talk of what many see as a pattern of Russians who run afoul of the Kremlin and later die under suspicious or criminal circumstances.
Glushkov was a director at Russian airline Aeroflot and Berezovksy's LogoVAZ auto company before he was charged and convicted of money laundering and fraud, for which he served 5 years in prison.
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Berezovsky fled to the United Kingdom in 1999 after he fell out with Vladimir Putin and Glushkov was charged with money laundering a fraud and spent five years in jail.
In 2013, Glushkov told the U.K.'s Guardian newspaper that he was skeptical that Berezovsky's death was a suicide.
"I'm definite Boris was killed". I have quite different information from what is being published in the media. He spent five years in jail in Russian Federation before escaping to the United Kingdom in 2004. He was supposed to have been appearing at court on Monday morning but failed to show up.
Russian media said he was granted political asylum in Britain in 2010.
British PM Theresa May says it's "highly likely" Russian Federation is behind the poisoning, and has given the country a deadline of Tuesday (UKT) to explain.
In a phone-call with British Prime Minister Theresa May today, US President Donald Trump assured the United Kingdom of support in the case.
Ako Mohammed, who runs a barber shop near Glushkov's home, said the Russian had last come in more than a fortnight ago.
Russian Federation denies any involvement in the March 4 attack on Skripal, 66, and his daughter Yulia, 33, who are both critically ill in hospital, and has accused Britain of unjustified action.
This is unedited, unformatted feed from the Press Trust of India wire.