DeMint was born in Greenville, South Carolina and educated at Wade Hampton High School in Greenville, the University of Tennessee and Clemson University. He owned a market research firm in Greenville.

When Fourth District Congressman Bob Inglis decided to honor a promise to serve only three terms and run against Senator Fritz Hollings, DeMint won the Republican primary for the district, which includes Greenville and Spartanburg, and easily won election in November. The district is considered the most Republican in the state, and he never faced serious or well-funded opposition.

DeMint declared his candidacy for the Senate on December 12, 2002 after Hollings decided to retire after the 2004 elections. He was supposedly the White House's preferred candidate in the Republican primary. Some thought DeMint was at a disadvantage since South Carolina had never elected two senators from the same region of the state. Lindsey Graham, South Carolina's other senator, was also from the Upstate. He placed a distant second in that primary on June 8, 2004, 18 points behind former governor David Beasley. However, he won a convincing victory in the runoff, and faced Democratic state education superintendent Inez Tenenbaum in November.

Tenenbaum led in many polls for much of the year. However, the state's strong support for George W. Bush gave DeMint enough of a push to defeat her by 9.6 percentage points in November. DeMint's win meant that South Carolina, long considered one of the most Republican states in the former Confederacy, was represented by two Republican Senators for the first time in its history.

DeMint is very conservative. He favors eliminating the IRS and Federal income tax. Additionally, while in Congress he sponsored legislation that would replace the current system with a 23ational sales tax on all goods and services. He claimed he had signed onto the legislation "to advance the debate" on tax reform, and that he did not specifically favor that version of reform over others.

The slogan of DeMint's 2004 Senate campaign was "Secure the Future," and he followed through on campaign pledges by staunchly supporting Social Security reform, and specifically private accounts within social security. DeMint is one of the most vocal supporters of "free trade and free markets," appropriate for a state which has prioritized foreign investment in its economy.

DeMint also stirred controversy during debates with Tenenbaum when he stated his belief that openly gay people should not be allowed to teach in public schools. When questioned by reporters, DeMint also stated that single mothers who live with their boyfriends should similarly be excluded from being educators. DeMint gave no reason why he felt this way, and it was speculated that he sat too far to the right of the mainstream, which caused Democrats to question his effectiveness as a potential Senator. He later apologized for making the remarks without specifically retracting their substantive claims, saying they were "distracting from the main issues of the debate." He also noted that these were opinions based on his personal values, not issues he would or could deal with as a member of Congress. He also favored banning all forms of abortion.

DeMint is a member of the Committee on Commerce, Science, and Transportation, the Committee on Environment and Public Works, the Special Committee on Aging, and the Joint Economic Committee. DeMint is currently the Deputy Majority Whip.