Senator Lindsey Graham, a South Carolina Republican who served in the State Legislature and the U.S. House of Representatives before being elected to the Senate four times, has died, his office announced early Sunday. He was 71.

He died of a “brief and sudden” illness on Saturday evening, his office said in a statement, without providing details.

Mr. Graham was first elected to the House of Representatives in 1994, before being elected to the Senate in 2002. He was re-elected to the Senate in 2008, 2014 and 2020.

Last month, Mr. Graham won the South Carolina Republican primary in his bid to serve a fifth term in the Senate, fending off five challengers.

“Senator Graham’s family appreciates prayers at this time and asks for privacy during this incredibly difficult period,” his office said in a statement.

Gov. Henry McMaster of South Carolina, a Republican, said in a statement that Mr. Graham was “the fiercest of fighters for South Carolina and America.” Mr. McMaster can immediately appoint a temporary replacement to fill Mr. Graham’s Senate seat through January. According to South Carolina law, an election for a full-term successor would be held in November.

Mr. Graham, who sought the 2016 Republican presidential nomination, built a reputation in Washington and abroad as one of the Senate’s most forceful advocates for an interventionist U.S. foreign policy. Throughout his career, he consistently argued for the use of American military power overseas, including most recently supporting aggressive military action against Iran. He also maintained close ties with Israel, making numerous visits there during his time in Congress.

Over his Senate career, Mr. Graham led two influential committees, Judiciary and Budget.

As head of the Judiciary Committee, he oversaw the confirmation of Amy Coney Barrett to the Supreme Court following the death of Ruth Bader Ginsburg. He also was a key figure in the 2016 fight over President Barack Obama’s nomination of Merrick Garland to the court, aiding in Republicans’ success in blocking the pick.

More broadly, Mr. Graham was instrumental in advancing President Trump’s effort to reshape the federal judiciary. During his tenure at the helm of the committee, the Senate confirmed more than 200 federal judges, including Ms. Barrett, cementing one of the defining conservative judicial legacies of the Trump era.

As chairman of the Budget Committee, Mr. Graham played a central role in translating Mr. Trump’s domestic agenda into legislation. He oversaw a budget resolution that allowed Republicans to advance much of the president’s sweeping tax, immigration and spending package without support from Senate Democrats.

The effort required months of negotiations among warring factions within his party before the tax package became law last year. Mr. Graham, along with Republican leaders and the Trump administration, embraced budget reconciliation as the party’s primary vehicle for enacting Mr. Trump’s agenda at a time when Republicans lacked the 60 votes needed to overcome a filibuster.

Once one of Mr. Trump’s sharpest Republican critics during the 2016 campaign, Mr. Graham later underwent a political transformation, becoming one of the president’s most steadfast and outspoken allies.

Mr. Trump offered condolences on social media early Sunday. “Senator Lindsey Graham, one of the greatest people and Senators I have ever known, is dead!” he wrote. “He was always working, and was a true American Patriot. Lindsey will be greatly missed!!!”

This is a developing story and will be updated.