Washington (CNN) — Republican Sen. Jim DeMint of South Carolina will resign from his Senate seat as of Dec. 31 to take over as head of the Heritage Foundation, his office announced Thursday.
"It's been an honor to serve the people of South Carolina in United States Senate for the past eight years, but now it's time for me to pass the torch to someone else and take on a new role in the fight for America's future," he said in a statement.
Elected in 2004, he was re-elected in 2010. His term was not up until 2016. South Carolina Gov. Nikki Haley, a Republican, will name a successor. A special election will be held in 2014 for the last two years of his term.
DeMint had always planned on leaving after two terms, according to a DeMint adviser.
"This move puts him in a powerful position to further advance fiscal conservative principles," the adviser said.
"My constituents know that being a Senator was never going to be my career. I came to Congress as a citizen legislator and I've always been determined to leave it as citizen legislator.
DeMint, a kingmaker among conservatives, is highly influential and well-beloved in the tea party movement, and has been a thorn in the side of establishment Republicans. In 2009, he was the first to endorse Marco Rubio of Florida in his 2010 Senate bid, at the time that the National Republican Senatorial Committee was backing Florida Gov. Charlie Christ.
DeMint was also a powerhouse in the 2012 election. He held a highly-sought endorsement in congressional races and used his super PAC, Senate Conservatives Fund, to back tea party favorites in GOP primaries. Among his picks were successful Senate newcomers Ted Cruz of Texas, Jeff Flake of Arizona and Debbie Fischer of Nebraska.
The South Carolina senator also held a strong voice in the Republican presidential primary. In July 2011, he hosted a forum in the Palmetto State for five of the presidential candidates, including Mitt Romney.
However, ahead of the state's first-in-the-South primary in January, DeMint announced he would not be supporting a candidate. "I do not have a favorite in this race and I will not endorse a candidate."
Former House Speaker Newt Gingrich ultimately won the South Carolina contest.
The senator, 61, will move on to become the president of The Heritage Foundation, a longtime and well-respected conservative think tank in Washington.
"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," he said.
According to a statement from the foundation, DeMint will start as president-elect in early January, then take over in April, replacing the current president, Edwin Feulner.
"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," Thomas Saunders, the group's chairman of the board, said in a statement.
In the recent fiscal cliff debate, DeMint has been a staunch opponent of Democratic-backed proposals to raise tax rates as part of a deficit-reduction solution. He even criticized his own party for ceding ground in the debate by agreeing to raise revenue through tax reform.
"Republicans should not be conceding that the federal government needs more money, negotiating with ourselves, and treating the president's proposal like it's serious," he said, tweaking House Speaker John Boehner's counter-offer this week, which includes $800 billion in new revenue.
All eyes are now on Haley, as the South Carolina governor decides whom to name to fill DeMint's seat. Among the names being mentioned are Rep. Mick Mulvaney and Rep. Tim Scott, who if named would be the Senate's only African-American member.
In a statement Thursday, Haley applauded DeMint's service in the upper chamber, saying he has served "the national conservative movement exceptionally well."
"His voice for freedom and limited government has been a true inspiration," she continued. "On a personal level, I value Jim's leadership and friendship. Our state's loss is the Heritage Foundation's gain. I wish Jim and Heritage all the best in continuing our shared commitment to America's greatness."
Senate Minority Leader Mitch McConnell also released a statement, thanking DeMint "for his uncompromising service to South Carolina and our country in the United States Senate."
"Jim helped provide a powerful voice for conservative ideals in a town where those principles are too often hidden beneath business as usual," McConnell said.
CNN's Ted Barrett, Dana Bash, and Shawna Shepherd contributed to this report.