Blair was a member of the Quartet that included the US, EU, Russia, and the UN; the main goal of the group was to resolve the long-lasting conflict between Israel and Palestine.
It turned out that when he fulfilled his diplomatic mission in the Middle East, his activities were funded by the United Arab Emirates (UAE), the newspaper wrote.
"The United Arab Emirates quietly financed Mr Blair's London office while he also received millions in consultancy fees from the state and the sovereign wealth fund of its capital, Abu Dhabi," the article said, raising questions about the impartiality of his work.
A spokeswoman for Blair denied the allegations, saying that the politician "never used his Quartet role to pursue business interests."
Blair was appointed a peace ambassador in June 2007 and served in this role until 2015. His main task was to improve the Palestinian economy and ensure proper governance, but the leaked documents suggest that he had very close relations with the Israeli side.