UPDATED 10:53 a.m. | Sen. Jim DeMint will resign from the Senate early next month to take the helm of the conservative think tank The Heritage Foundation, The Wall Street Journal first reported Thursday morning.

The South Carolina Republican, who was first elected to the Senate in 2004, has been a driving force among the conservative Republican Party base and the tea party movement. And he has often been a thorn in the side of Senate GOP leadership by supporting conservative primary candidates in 2010 and 2012 who later had trouble winning general elections.

“I’m leaving the Senate now, but I’m not leaving the fight,” DeMint said in a statement. “I’ve decided to join The Heritage Foundation at a time when the conservative movement needs strong leadership in the battle of ideas. 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.”

The move came as a surprise on Capitol Hill, where the senator was in line to take over as ranking member of the Commerce, Committee next year, with aides already raising questions about how well he would work with Chairman Jay Rockefeller, D-W.Va.

South Carolina law allows the governor, Republican Nikki R. Haley, to make an appointment to fill DeMint’s unexpired term, in a state that would be safe Republican territory either way.

In an interview with the Wall Street Journal announcing the move, DeMint, who had already said he would not seek another Senate term, indicated he still had work to do politically, but thought that the timing was right.

“This really gets my blood going again thinking about the possibilities. This is the time to elevate the conservative cause,” he said.

“Jim DeMint has shown that principled conservatism remains a winning political philosophy. His passion for rigorous research, his dedication to the principles of our nation’s founding, and his ability to translate policy ideas into action make him an ideal choice to lead Heritage to even greater success,” Heritage Chairman of the Board Thomas A. Saunders told employees this morning, according to the organization.

Fellow conservative GOP Sen. Patrick J. Toomey of Pennsylvania was among the first offer words of encouragement.

“Jim is not just a colleague; he is a friend and a mentor, and his departure will be a tremendous loss for the U.S. Senate and for the conservative movement. In eight years, he has personally led the effort to change the composition of the Senate for the better, and provided consistent and principled leadership in the fight for liberty and limited government. He will be missed,” the former Club for Growth president said in a statement. “I’m confident he will continue to play an important role in the ongoing public debate about the future of this country, and I wish him the best in his new position.”