Mohamed Amersi has given nearly £525,000 to the party since 2018.
Leaked documents reveal how he worked on a series of controversial deals for a Swedish telecoms company, Telia, that was later fined $965m (£700m) in a US prosecution.
Mr Amersi denies any wrongdoing. The 61-year-old is a corporate lawyer who worked as a consultant for Telia between 2007 and 2013.
Working with the International Consortium of Investigative Journalists and the Guardian, BBC Panorama has obtained documents that show how Mr Amersi was involved in a controversial $220m payment to a secretive offshore company in 2010.
The firm was controlled by Gulnara Karimova - the daughter of the then president of Uzbekistan - and the payment was described by the US authorities as a “$220m bribe”.
Mr Amersi’s lawyers said the offshore company had been “vetted and approved by Telia” and that its involvement “did not raise any red flags” to him.
Questions about the sources of Mr Amersi’s wealth come as the Conservative Party’s annual conference is under way in Manchester.
His donations have included more than £100,000 towards the 2019 general election campaign and £10,000 to the prime minister’s leadership bid.
Mr Amersi’s Russian-born partner, Nadezhda Rodicheva, has also donated money to the Conservatives - more than £250,000 in 2017 and 2018.
At the moment individual donors only need to be on the UK electoral register. Once a party has checked that, they can accept as much money as they like.
In recent months, Mr Amersi has been drawn into a “cash for access” row centred around claims that high-spending Tory donors were able to gain regular meetings with the prime minister and chancellor.
Amersi, of course, allegedly paid £100,000 for “Breakfast With Boris” …