The 52-year-old, who left his position in the Obama administration in January, will begin his new full-time job with the New York-based Warburg Pincus LLC in March of 2014.
According to the newspaper, Geithner will not serve as a figurehead or advisor, like many former government heads who made the leap into private enterprise.
Much more will be expected of Geithner, who will play a central role in the company's strategizing and daily management, the report said.
"It was clear that they wanted me to play a substantial role," said Geithner, who was one of the architects of the bank rescue programme during the financial crisis.