Updated 11:20 a.m.
Sen. Jim DeMint, R-S.C., announced Thursday that he will resign from the Senate in January and become president of the Heritage Foundation, a conservative think tank.
"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."
The 61-year-old DeMint, South Carolina's junior senator, was first elected to the House in 1998. After serving three terms, he was elected to the Senate in 2004 and reelected in 2010.
South Carolina's Republican governor, Nikki Haley, will name a successor to DeMint, who will then compete in a special election in 2014. "South Carolina has a deep bench of conservative leaders and I know Governor Haley will select a great replacement," DeMint said in the statement.
DeMint is among the most conservative members of the Senate, and has clashed at times with the rest of the GOP. The tea party-aligned self-described "citizen legislator" has pushed for a balanced budget amendment to the Constitution, strongly opposed abortion rights and same-sex marriage, and calls the national health care law and the bail out of Wall Street "unconstitutional power grabs" by the government.
DeMint told the Wall Street Journal, which broke the news shortly before DeMint released his statement, that the decision was grounded in the need to effectively popularize conservative positions "because we saw in the last election we were not able to communicate conservative ideas that win elections."
DeMint, who had previously said he planned to leave the Senate in 2016, will replace Ed Fuelner as president of the Heritage Foundation.
South Carolina's senior senator, Lindsey Graham, is up for reelection in 2014, as is Gov. Haley. That means the state will have two Senate races and a governor's race in the 2014 cycle.
A South Carolina Republican source, who asked that his or her named not be used, told CBS News that South Carolina Rep. "Tim Scott is the undisputed favorite - and probably preferred by Jim DeMint."
"It would be historic for an Indian American governor from the Deep South to appoint an African American to the US Senate," said the source. "I think it's highly unlikely she would appoint a placeholder. There are too many critical votes coming in the next 24 months. Scott and DeMint are lock step on the issues."
The source added that if Haley does appoint a placeholder, the favorites are former South Carolina attorney general Henry McMaster and former South Carolina House Speaker David Wilkins.
In a statement, South Carolina Republican Party Chairman Chad Connelly called DeMint a "conservative rock star."
"Jim DeMint is a small businessman who ran for Congress to change the way Washington works," he said. "Without question, he succeeded."
Haley said DeMint "has served South Carolina and the national conservative movement exceptionally well."
"His voice for freedom and limited government has been a true inspiration," she continued in a statement. "On a personal level, I value Jim's leadership and friendship. Our state's loss is the Heritage Foundation's gain."
And Senate Republican Leader Mitch McConnell said DeMint "helped provide a powerful voice for conservative ideals in a town where those principles are too often hidden beneath business as usual."
With reporting by CBS News' Caroline Horn.