Saeb Erekat, a top Palestinian negotiator who helped craft some of the most sweeping bids for Arab-Israeli peace but was left dismayed by both Israeli resistance to key concessions on land and Palestinian infighting that eroded his people’s unity, died Nov. 10 at a hospital in Jerusalem. He was 65.

The cause was complications from covid-19, according to his office and family. He had a heart attack in 2012, and five years later, he received a lung transplant in Virginia to treat pulmonary fibrosis. He announced early in October that he had tested positive for the coronavirus and was rushed to the Israeli hospital from his home in Jericho on Oct. 18. He was placed on a ventilator the next day.

Dr. Erekat, who honed his fluent and idiomatic English during studies in San Francisco and Britain, was for decades a principal international voice of the Palestinian cause. Even as peace efforts faltered in the late 1990s, he remained a fervent backer of the “two-state solution” in which a Palestinian nation would exist side by side with Israel.

Yet Dr. Erekat also shared the deepening Palestinian frustration as aspirations of statehood appeared to slip further away after a flurry of optimism generated by the landmark Oslo accords of the 1990s.

The agreements — hammered out by representatives including Dr. Erekat, when he was a protege of Palestine Liberation Organization leader Yasser Arafat — expanded Palestinian autonomy in the West Bank and Gaza Strip. Additional gains fell apart amid the second of two Palestinian uprisings against Israel, known as intifadas, and the construction of Israel’s “separation barrier” with the West Bank.

When asked in 2015 if the optimism of Oslo was lost, he told the BBC: “It aches my heart to say yes.”

The Palestinians, while blaming Israeli leaders, were also weakened by a family feud. The main Fatah party was left in control of the West Bank while the militant group Hamas held the Gaza Strip, which came under an Israeli blockade and retaliatory attacks.

Dr. Erekat temporarily resigned his negotiator post in 2003 after being left off a team led by future Palestinian president Mahmoud Abbas, who was engaged in a power struggle with Arafat (who died in 2004). Dr. Erekat stepped down again in early 2011 after the leak of the “Palestine Papers,” which detailed years of confidential exchanges in the peace process and in which Dr. Erekat at times assailed Hamas.

Hamas and other critics portrayed Dr. Erekat as feckless and timid for standing against militants carrying out anti-Israel attacks — acts that some Palestinians saw as heroic.

Still, Dr. Erekat retained senior posts within the PLO and, for a time, was mentioned as a possible successor to the aging Abbas. He met with every Israeli leader over the past three decades and with hundreds of diplomatic envoys, including U.S. State Department officials who tried, and failed, to revive peace talks.

“Erekat was the organizational memory of the whole negotiating process for the Palestinians,” said Gilead Sher, who served as chief Israeli envoy at talks from 1999 to 2001.

Dr. Erekat could shift easily from strident to irreverent and back again — giving him a rare disarming touch amid the bluster and suspicion of Israeli-Palestinian talks.

One minute, he might rail against Israeli settlements in the West Bank. Then he could offer comic relief with a quip about his Sisyphean fate.

“I try my best to understand the Israelis’ fears and aspirations, but they can get too complicated for me,” he told the New York Times in 2007. “Every day there’s something going on, like the cats outside my window at night, and I never know if they’re making love or fighting or both.”

Saeb Muhammad Salih Erekat was born April 28, 1955, in Abu Dis, a Palestinian town near Jerusalem that was then under Jordanian control. His family later moved to Jericho. His father ran a bus company that was wiped out during the 1967 war that left Israel in control of the West Bank, plunging the family into financial despair.

“There was no such thing as insurance against wars, so my father lost everything,” he later told an interviewer. Dr. Erekat joined Palestinian protests as a teen, scrawling anti-Israel graffiti and throwing rocks at Israeli soldiers.

He headed to the United States in 1972 for university studies, following in the footsteps of an older brother.

Supporting himself working nights at a Palestinian-owned deli, Dr. Erekat graduated from San Francisco State University with a bachelor’s degree in 1977 and a master’s degree in 1979, both in international relations. He was elected president of the Arab Students Association.

After receiving a doctorate in conflict resolution studies in 1983 at the University of Bradford in England, he returned to Jericho and joined the editorial board of the leading Palestinian-run newspaper, al-Quds.

Already he was on the radar of Israeli security. A few years earlier, as a lecturer at An-Najah National University in Nablus, he had written an article calling for greater dialogue between Israeli and Palestinian academics. Students boycotted his classes and circulated petitions calling him a traitor to the Palestinian cause.

In response, Dr. Erekat invited Israeli university students to his classroom, provoking an Israeli military commander to complain that such appeals were causing rifts among Israelis. “To hell with them and to hell with you,” he told the commander, according to an account in the San Francisco State University alumni magazine. “Nobody will intimidate me.”

During the first intifada — a wave of unrest from 1987 to the early 1990s — Israeli authorities placed Dr. Erekat under house arrest. He also attracted the attention of the PLO, joining its brain trust as a suit-and-briefcase counterpoint to Arafat’s military fatigues and sidearm.

At the Madrid peace talks in 1991, Dr. Erekat stunned Israelis by showing up wearing a traditional black-and-white checked kaffiyeh head covering as a statement of Palestinian solidarity. The Israeli delegation almost walked out.

The display was Dr. Erekat’s grand entrance on the international stage. He became the senior representative in nearly every major subsequent negotiation, including the Oslo meetings and Camp David talks in 2000.

He was a quote machine for foreign correspondents and a regular on international news channels. He jetted from one gathering to another — in Davos, London, at the United Nations — usually dressed impeccably in a dark suit, a smart tie and a Palestinian flag lapel pin.

The only way to stop the cycle of violence, he told the San Francisco alumni magazine, was through a “meaningful peace process.”

“As a Palestinian father, I want my children to be journalists and schoolteachers and professors and musicians,” he said. “I don’t want them to be suicide bombers. But in order to do so, I need to provide hope that they will live in freedom away from occupation.”

A stinging blow for Dr. Erekat was the unraveling of the “road map for peace,” a step-by-step plan floated in 2003 that could have cleared the way for a Palestinian state. But he was an equal opportunity blame-caster.

He denounced the Palestinians for failing to seize the moment and curb anti-Israel violence. He lashed out at the United States, one of the road map’s powerful international backers, for failing to press its Israeli allies to live up to the accord. And he dismissed Israeli leaders as untrustworthy hard-liners who had no intention of following through with promised land concessions.

“I came to the conclusion,” he told Newsweek in 2003, “that it will be easier for the pope to cancel Christmas Mass than for [then-Israeli Prime Minister Ariel] Sharon to accept the road map.”

Dr. Erekat remained a key international voice for the Palestinians as the Trump administration shattered past White House policy by moving the U.S. Embassy from Tel Aviv to Jerusalem in 2018. Later, the United States helped broker diplomatic deals with Gulf Arab states, the United Arab Emirates and Bahrain, to open ties with Israel — shifts that Palestinians perceived as collateral blows.

As other countries followed the U.S. lead to open embassies in Jerusalem, Dr. Erekat expressed frustration at the relative silence from many of the Palestinians’ professed allies in the Muslim world.

“Where are the Arab and Islamic countries?” he tweeted in September. “Isn’t that a good question to those who say they’re concerned for Palestine?”

Dr. Erekat and his wife, Naama, had twin daughters and two sons. A complete list of survivors was not immediately available.

Even as his health began to slip, Dr. Erekat spoke for the Palestinians and wrote books on politics and conflict resolution. He often found dark humor in the lopsided nature of the Israeli-Palestinian relationship.

Israel, he pointed out, boasted a huge military and backing from Western powers. The Palestinians, meanwhile, had few resources and almost no leverage. As their representative, he called himself “the most disadvantaged negotiator since Adam negotiated Eve.”

Ruth Eglash in Jerusalem contributed to this report.