Senator Lindsey Graham had been a fixture of South Carolina politics since 1994, climbing the ranks in his home state before catapulting to the forefront of Congress, even making a bid for the Republican presidential nomination in 2016.

On Sunday, stunned by the news of Mr. Graham’s sudden death overnight, South Carolina leaders began mourning him. His political shape-shifting had at times confounded many, but it had positioned Mr. Graham to keep sending millions of dollars home and keep the state represented in some of the world’s most powerful rooms.

“We shall not see his likes again,” said Gov. Henry McMaster, a Republican, who called Mr. Graham “irreplaceable” in a statement early Sunday.

Attorney General Alan Wilson, who is widely expected to succeed Mr. McMaster in the governor’s mansion as the Republican nominee, said Mr. Graham had “carried our state’s values with him everywhere he went.”

“He could fill a room with stories, make you laugh when you needed it most, and somehow find the right joke even in the middle of the most serious conversations,” Mr. Wilson said in a statement. “That wit was matched by an unwavering loyalty to his friends and a generosity that many people never saw.”

As the Republican Party lurched rightward, particularly as President Trump took hold of the party, he was not always beloved by the increasingly right-wing conservative base. Those voters mistrusted his record of willingness to work with Democrats, as well as his consistent support for aggressive military action abroad and early criticism of Mr. Trump during the 2016 campaign.

But last month, Mr. Graham had easily held off a cluster of primary challengers.

“I hope that South Carolinians will join me in setting partisanship aside and offering gratitude to Senator Lindsey Graham for his service to the great state of South Carolina,” said Dr. Annie Andrews, the Democratic nominee who had been set to face Mr. Graham in the November election.

Mr. Graham’s death at 71, barely a month after he clinched another primary win to serve another six years in the Senate, is now likely to set off an unexpected round of political jockeying.

South Carolina law allows Mr. McMaster the chance to appoint a temporary successor to complete Mr. Graham’s term, which runs through Jan. 3, 2027. A special Republican primary election would be held next month, ahead of the November election.

But, at least for a few hours on Sunday, Republicans focused on paying tribute to Mr. Graham and his legacy.

“South Carolina lost a statesman,” Senator Tim Scott said. “And I’ve lost a friend.”

This is a breaking news story and will be updated.