Sen. Jim DeMint, the Tea Party favorite who riled moderate Republicans this week by bashing House Speaker John Boehner's "fiscal cliff" proposal, announced his surprise resignation from the Senate on Thursday.
In a statement, he said he will leave in January to become president of conservative Heritage Foundation think tank.
"I'm leaving the Senate now, but I'm not leaving the fight," DeMint said in his statement. "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."
The 61-year-old South Carolina Republican was first elected to the Senate in 2004. He previously served in the U.S. House for three terms.
Earlier this week, DeMint denounced the $800 billion in higher tax revenue over 10 years that would come from Boehner's plan, calling it a "tax hike" that will "destroy American jobs and allow politicians in Washington to spend even more" — while failing to reduce the debt. (Read More: Obama Says Tax Rate Cut for Wealthy Possible.)
Boehner's plan was the Republican response to a White House plan last week that includes $1.6 trillion in higher taxes over a decade.
The House GOP counterproposal also included an increase in the eligibility age for Medicare, and lower cost-of-living hikes for Social Security benefits. Overall, the plan is designed to save $2.2 trillion over 10 years. (Read More: How the Plans Differ)
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. and wouldn't let the process drag out. Haley didn't specify anyone she favored to replace DeMint, but did take one name out of contention.
"I will not be appointing myself. That's not even an option," Haley told WORD-FM.