COLUMBIA, S.C. — Republican U.S. Sen. Jim DeMint, a tea party favorite known for bucking party leaders to back challenges to centrist veterans he didn’t view as conservative enough, said Thursday he was resigning to take the helm of a conservative think tank.

The South Carolina lawmaker said in a statement he was stepping down to become president of the Heritage Foundation. His office said his resignation is effective Jan. 1.

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Sen. Jim DeMint: "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," AP

DeMint was first elected to the Senate in 2004 and easily re-elected six years later. He previously served in the U.S. House of Representatives for three terms.

“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,” DeMint, 61, said in a statement.

DeMint didn’t respond to an interview request from the Associated Press.

His job with the foundation starts Jan. 3, but DeMint won’t officially become president until April 3, when founder Edwin Feulner retires, said foundation spokesman Jim Weidman.

DeMint’s resignation comes a day after the foundation board voted to make DeMint the next president. The senator began talking with the committee that was choosing Feulner’s replacement several months ago, Weidman said.

Republican Gov. Nikki Haley will appoint DeMint’s Senate successor. She told a Greenville talk radio station she plans to pick someone who will fight for conservative ideas. She said she wouldn’t let the process drag out. Haley didn’t specify anyone she favored to replace him, but did take one name out of contention.

“I will not be appointing myself. That’s not even an option,” Haley told WORD-FM.

DeMint’s former state director, Luke Byars, said the senator’s new role will allow him to effect change outside the U.S. Capitol. In the fall election, Democrats strengthened their majority in the Senate.

DeMint, who previously ran a marketing firm, thought conservatives didn’t do a good job communicating their message in the presidential race, Byars said.

“He knows how to communicate,” said Byars, a political consultant. “This is a vehicle for him to push and pull on conservative issues on a national stage, to get the attention of folks inside Washington.”

The resignation of DeMint, a Greenville native, will have a ripple effect on the state GOP leadership.

Whomever Haley appoints would face a special election in 2014 to finish DeMint’s term, which expires in 2016. U.S. Sen. Lindsey Graham, DeMint’s Republican colleague from the state, faces re-election in 2014.

South Carolina GOP Chairman Chad Connelly said DeMint redefined how the U.S. Senate worked, taking principled stands against party leaders.

“He’s been a conservative rock star,” Connelly said. “I’m sure the conservatives in South Carolina will be heartbroken.”

DeMint never was much for compromise in the U.S. Senate. He said plenty of times he would rather stand with a committed minority than a big-tent majority.

DeMint’s positions have earned him rankings as one of the most conservative senators. He supported partially privatizing Social Security and installing a flat sales tax to replace income taxes. He once suggested that gays and unwed pregnant women should not teach in public schools.

DeMint has ties to, but no longer runs, the Senate Conservatives Fund, which ranked sitting senators. He formally cut ties with the political action committee he founded earlier this year.

He helped raise more than $25 million for the fund for the 2010 and 2012 elections.

DeMint also wasn’t shy about going after people in his own party if he thought they weren’t conservative enough.

He opposed longtime Sen. Arlen Specter of Pennsylvania, just before the veteran Republican, facing a challenge from the right, switched to become a Democrat. DeMint also broke with Senate Minority Leader Mitch McConnell in the Republican leader’s backyard to support tea party favorite Rand Paul in the Kentucky Senate primary. Both Paul and Pat Toomey, the conservative who won the GOP nomination in Pennsylvania, were elected in 2010.

DeMint was elected to the U.S. House in 1998 and to the U.S. Senate in 2004, replacing Ernest “Fritz” Hollings. DeMint easily won re-election in 2010 with almost no in-state campaigning. He defeated Democrat Alvin Greene, an unemployed political unknown, with 61 percent of the vote, as he focused on Senate races outside South Carolina.

Graham said the resignation of his friend surprised him.

Graham, who is viewed as more moderate than DeMint, acknowledged his differences with him during comments on the Senate floor, but said they had both represented the state well in different ways.

“I think we’ve done a pretty darn good job for South Carolina, at times playing the good cop, the bad cop, but always trying to work together,” Graham said. “What differences we’ve had have been sincere, and that’s the word I would use about Sen. DeMint. … We’ve had a great ride together.”