DeMint's Washington office confirmed Thursday that the South Carolina politician is stepping down to become president of the Heritage Foundation, effective Jan. 1.
His office said DeMint was too busy to come to the phone.
The 61-year-old Republican was first elected to the Senate in 2004.
Republican Gov. Nikki Haley gets to appoint his Senate successor.
His former state director Luke Byars says the new role allows DeMint to effect change outside of the U.S. Capitol.
The political consultant says it's a vehicle for him to push and pull on conservative issues on a national stage.