Police said Nikolai Glushkov’s death was being treated as “unexplained” and his family have been informed.
A spokesperson for the Metropolitan Police said its counter-terrorism command was leading the investigation “as a precaution because of the associations that the man is believed to have had”, but there was no immediate evidence of a link to the Salisbury nerve agent attack.
Officers were called by the London Ambulance Service at 10.46pm on Monday to reports of a man found dead at his home in Clarence Avenue, New Malden.
“A post-mortem examination will be held in due course,” Scotland Yard said. “The death is currently being treated as an unexplained.”
The 68-year-old was a close friend of exiled Russian oligarch Boris Berezovsky, who was himself a friend of murdered spy Alexander Litvinenko.
Mr Berezovsky was found hanged in the bathroom of his Berkshire home in 2013.
Police said a post-mortem showed no sign of a violent struggle, and an inquest recorded an open verdict after hearing conflicting evidence.
At the time, Mr Glushkov said he believed his friend had been murdered, telling The Guardian: “I don't believe Boris died of natural causes. Too many deaths [of Russian exiles] have been happening.”
Friends of Mr Glushkov were posting news of his death on social media, while his lawyer confirmed his passing to Russia's Business FM radio station.
He served a five-year term for money laundering and fraud in Russia, then fled the country after being handed a two year suspended-sentence for fraud in 2006.
Last year, he was sentenced to eight years imprisonment and a million-Ruble fine in absentia for allegedly defrauding Aeroflot.
Mr Glushkov worked as the First Deputy General Director for Russia’s flag carrier in the late 1990s, having worked for Mr Berezovsky’s LogoVAZ car company.
His LinkedIn page listed him as a “private consultant” in financial services since 2011.
The Home Office said it was aware of Mr Glushkov's death but would not comment on the ongoing police investigation.
The Russian Embassy told The Independent "nobody had been in touch with the embassy regarding the death of Mr Glushkov".