Akinyemi Adigun, 35, convinced a woman in her 70s to give him almost £10,000 which he promised to pay back.
But Adigun, of Moston, Manchester, never repaid the money and stopped contacting the victim after he had drained her life savings.
Now Adigun is facing jail after he was found guilty on Friday by a unanimous verdict of possessing criminal property following a trial at Warwick Crown Court.
He had told the victim, who had lost her husband three years earlier, he was called Dr Marcus Harry and was a British medic working in Nepal.
Prosecutor Daniel Wright told the court the victim, from Leamington Spa, Warwickshire, fell for Adigun after joining a dating website for widows in September 2015.
He said: "She found herself getting lonely and, at the suggestion of a friend, she joined a dating site for widows.
"She was contacted by 'Dr Marcus Harry,' who said he was a 50-year-old male from Bristol who was working overseas in Nepal.
"They hit it off, and within a month Dr Marcus Harry starts to ask for money from her. At first these were small amounts.
"It began with a request over WhatsApp, asking her if she would mind getting him £50 of iTunes vouchers which he said he was unable to get hold of in Nepal.
"She agreed, and bought a £50 voucher at Argos in Leamington before photographing it and sending the picture to him by email.
"Two weeks later Dr Harry told her he was planning to fly back to the UK on October 17, but was unable to get hold of the £1,000 he needed for the flight - so she agreed to send it to him on the basis that he would repay it on his return."
The court heard the money was transferred into the account which belonged to a woman called Jayne Chew, from Burnley.
The victim also sent Adigun another £50, supposedly so he could top up his mobile phone.
Mr Wright said: "A few days later there were further requests.
"This time Dr Harry asked for £4,000 on the fifth of October because he said he had been fined for bringing gold into Dubai on his way back and would not be released until he had paid a £25,000 fine."
The court heard the victim reluctantly transferred the £4,000 to the account of a co-defendant, Dare Moyo.
The woman then received a message from "Dr Harry" claiming he had not been able to raise the rest of the money, and persuaded the woman to transfer a further £4,000 which was paid into Adigun's account.
Mr Wright said: "The prosecution say that what happened was a fraud, that she was duped, so whatever money flows from that is criminal property."
Adigun was bailed and will be sentenced at a later date.