Even as the wars in Gaza and Iran eroded American support for Israel, Lindsey Graham remained one of the country’s staunchest allies in Washington.

Mr. Graham, the Republican senator from South Carolina who died on Saturday, was a prominent lobbyist in Washington for the joint U.S.-Israeli war against Iran, which began in late February.

In recent years, Mr. Graham’s interventionist foreign policy views grated with some in the Republican Party, which grew more suspicious of U.S. global entanglements. But those views won him plaudits in Israel, where Mr. Graham was celebrated as a steadfast supporter amid the country’s deepening international isolation.

On Sunday, Benjamin Netanyahu, the Israeli prime minister, called Mr. Graham a “great friend of Israel” who “understood that the security of Israel and America are inseparable.” In the weeks leading up to the war in Iran, Mr. Graham traveled to Israel at least twice to meet Mr. Netanyahu to discuss the matter.

“Israel has lost one of its greatest friends. America has lost a great patriot. I have lost a beloved friend,” Mr. Netanyahu said in a statement.

Several of Mr. Netanyahu’s opponents — including those running against him in parliamentary elections later this year — joined him in mourning the senator.

Gadi Eisenkot, a former Israeli military chief of staff who has recently emerged as the front-runner in the campaign to unseat Mr. Netanyahu, called Mr. Graham “one of the greatest friends Israel and the Jewish people have ever known.”

“His tireless work made the U.S.-Israel alliance stronger, the Middle East safer and the world more secure,” Mr. Eisenkot said in a statement.

For a U.S. senator, Mr. Graham had an unusually heavy focus on the Middle East, frequently traveling to the region to meet with leaders, including President Abdel Fattah el-Sisi of Egypt and Mohammed bin Salman, the crown prince and de facto ruler of Saudi Arabia.

One of Mr. Graham’s major foreign policy goals was to broker a U.S.-backed deal to normalize Israel’s relations with Saudi Arabia, occasionally shuttling between the Saudi capital, Riyadh, and Jerusalem.

Before the Hamas-led attack on Israel on Oct. 7, 2023, which ignited the war in Gaza, President Joseph R. Biden Jr.’s team worked for months to normalize relations. One incentive for the Saudi government to agree: a defense treaty with the United States.

The treaty would have required approval in the Senate. Mr. Graham aimed to convince Senate Republicans to vote for the treaty agreement, even though it would have delivered a diplomatic victory for the Democratic administration, said Mike Herzog, who served as Israel’s ambassador to Washington during the Biden presidency.

“The idea was that Biden would bring the Democrats and Lindsey would bring the Republicans,” said Mr. Herzog, now a fellow at the Washington Institute for Near East Policy, a research group. “He was very dedicated to the Israeli-Saudi issue, and he believed that it was good for the United States as well.”

U.S. and Israeli hopes for an agreement with Saudi Arabia largely faded after Israel’s military campaign against Hamas in Gaza, which has killed tens of thousands of Palestinians, prompting international condemnation.

The devastating war exacerbated a sea change in public opinion in the United States, eroding long-held bipartisan support for the Israeli government.

“Israel’s image is worsening in the United States across the board, among Republicans as well as Democrats. But Lindsey remained very firm in his support, one of the most prominent voices for the U.S.-Israeli alliance,” Mr. Herzog said.

Some Iranian media linked to the government appeared to celebrate Mr. Graham’s death. Tasnim, an outlet close to Iran’s powerful Islamic Revolutionary Guards Corps, said he had become “food for snakes and ants,” while the Islamic Republic was still standing.

Sanam Mahoozi and Heedo Abu Laban contributed reporting.