Sen. Jim DeMint (R-S.C.) will leave the U.S. Senate next year to become president of the Heritage Foundation, succeeding Edwin Feulner, who first co-founded the conservative think tank in 1973 and has served as president for the past 36 years.

“I’ve decided to join The Heritage Foundation at a time when the conservative movement needs strong leadership in the battle of ideas,” DeMint said in a statement. “My constituents know that being a Senator was never going to be my career.”

“I couldn’t be more pleased with the Board’s selection,” Feulner said in a statement.  “Jim DeMint understands that conservative principles and values advance the interests of all Americans—regardless of age, gender, wealth or race.  He is firmly committed Heritage’s immutable mission: to build an America where freedom, opportunity, prosperity and civil society flourish.”

The decision contradicts the expectations of many who thought former Dick Cheney aide David Addington would be named Heritage’s next president.

At a meeting on Wednesday, Heritage’s Board of Trustees unanimously chose DeMint as the organization’s next leader, starting April 3, with a transition period beginning in early January so Feulner and DeMint can work side-by-side. After April, Feulner will continue serving as chancellor of Heritage and chairman of the Asian Studies Center.

According to Heritage, Feulner conveyed to the board three years ago his intentions to step down on his 35th anniversary and tasked senior management at the think tank with developing a succession plan.

A subset of the board managed the process with DeMint coming into the search earlier this year.

Feulner’s decision to step down is the newest among longstanding leaders in some of Washington’s most prominent think tanks, which has created a major wave of new presidents.