South Carolina Sen. Jim DeMint is leaving Congress to head the conservative Heritage Foundation.
The Tea Party-backed senator announced the move Thursday, saying he will step down from the Senate in January to become president of The Heritage Foundation think tank. He plans to formally start the new job in April.
"I'm leaving the Senate now, but I'm not leaving the fight. I've decided to join The Heritage Foundation at a time when the conservative movement needs strong leadership in the battle of ideas," he said in a statement. "No organization is better equipped to lead this fight and I believe my experience in public office as well as in the private sector as a business owner will help Heritage become even more effective in the years to come."
DeMint later told Fox News that "I honestly believe I can do a lot more on the outside than on the inside."
DeMint has been an outspoken voice in the Senate for its most conservative wing, most recently chiding House Republican leaders for offering to put revenue on the table as part of negotiations over the looming fiscal crisis.
He was elected to a second term in the Senate in 2010. His departure sets up a succession battle in South Carolina. South Carolina Gov. Nikki Haley would choose a replacement, who would then have to run in a special election in 2014.
One member of the South Carolina congressional delegation told Fox News the move was seen as a "total surprise."
DeMint will replace outgoing president Ed Feulner at Heritage. Heritage Board Chairman Thomas Saunders said in a statement that DeMint "has shown that principled conservatism remains a winning political philosophy."
While DeMint has occasionally raised hackles among Republicans, conservative lawmakers and groups praised DeMint's qualifications.
Fellow South Carolina Sen. Lindsey Graham said he's "very disappointed" that his long-time friend and colleague is resigning.
"The Senate's loss is Heritage's gain," Graham told Fox News Radio.