Theerapong Poopan, 35, said the wallet was dropped on the backseat of his car after he drove a group of Thais and Japanese from Asok to Silom on Wednesday night. He then found out that the wallet belonged to Yasuyuki Takashi, 49.
Mr Theerapong called the Traffic Radio Society FM 99.5 to get help in finding Mr Takashi. The station then contacted a hotel near where the passengers got off and eventually was able to contact the man.
Mr Takashi said he works as an architect and came to Thailand on vacation. He said he felt delighted as he did not expect to get his wallet back.
He gave the taxi driver 18,000 baht as a token of gratitude.