The Council on Foreign Relations said Geithner had accepted a position as a senior fellow and would start later this month.
The Los Angeles Times reported Wednesday that Geithner has previous experience at the think tank, having worked there in 2001 after an earlier job at the Treasury Department.
After his previous stint at the think tank, Geithner went on to a job at the International Monetary Fund. From there, he went on to serve as president of the Federal Reserve Bank of New York.
He worked in that job from 2003 through 2009, when he became the treasury secretary.
"Both at treasury and at the New York Federal Reserve, Tim was a tireless, creative, and responsible custodian of the public trust," said the think tank's president, Richard Haass.
"His coming to CFR only strengthens our capacity to produce thoughtful analysis of issues at the intersection of economic, political, and strategic developments," Haass said.