Negotiators announced on Wednesday that they had reached an agreement on a ceasefire for the war in the Gaza Strip, 15 months after the devastating Hamas-led assault on Israeli soil launched a relentless military campaign with few parallels in recent history.

In the attack that started it all, the October 7, 2023 attack on southern Israel led by Hamas fighters, killed about 1,200 people, most of them civilians, which stunned Israelis. In the months that followed, an estimated 45,000 Palestinians in Gaza, many of them civilians, were killed and entire towns razed to the ground.

On Wednesday, Gazans allowed themselves to hope for an end to long months of hunger, destruction and fear, as Israelis anxiously prepared to welcome home dozens of men and women taken hostage by Hamas during the 2023 attack.

According to the conditions temporary agreementreached in the final days of the Biden administration, the Israeli military will begin withdrawing its forces and Hamas will begin freeing some of the hostages captured during the bloody campaign that started the war. If approved by the Israeli government, the ceasefire will take effect on Sunday.

“An entire country is holding its breath tonight,” said Yair Lapid, the leader of the centrist opposition in Israel, where the government is expected to vote on the deal on Thursday.

Hamas said in a statement: “This is a historic moment in the conflict with our enemy.” It lauded the “legendary resilience” of Gazans in the face of a war that has sparked a humanitarian crisis. One of the group’s leaders also praised the Hamas-led attack that sparked the war, despite the bitter price paid by Palestinians.

Even amid warnings that some of the deal’s details were still being worked out, celebrations broke out in both Gaza and Israel on Wednesday.

“Glory be to God, this tragedy is over,” said one Gaza City resident, Mohammad Fares, 24, as celebratory booing and gunfire rang out in the background.

But in a decimated Gaza that bears little resemblance to the enclave that existed before Israel launched a sweeping offensive aimed at destroying Hamas once and for all, sadness and anguish, not joy, remain the dominant emotions among Palestinians.

“How can we ever rebuild?” asked Suzanne Abu Daqqa, who lives in a suburb near the southern Gaza city of Khan Younis. “Where do we even begin?”

In Israel, the families of the hostages issued a statement announcing their “tremendous joy and relief” at the deal, but also expressed “deep anxiety and concern” that some hostages may be left behind. Of the approximately 250 people arrested in Israel on October 7, 2023, about 100 are still in Gaza; about a third are believed to have died in captivity.

Even as the temporary ceasefire was celebrated, some appeared to be trying not to overestimate what could be achieved. In announcing the deal, Qatar’s prime minister, Mohammed bin Abdulrahman al-Thani, spoke of “sustainable peace.”

The agreement, however, was a major breakthrough after months of talks that often seemed close to a solution, only to fall apart. President Biden’s administration pressed for a truce as the clock ticked down on his time in office.

“Too many innocent people have died, too many communities have been destroyed,” said Mr. Biden to reporters at a press conference.

His successor, President-elect Donald J. Trump, had threatened with serious consequences unless Israel and Hamas reach an agreement before his inauguration on January 20, and Mr. Biden suggested yes The White House consulted with Trump’s team about conversations.

“We are handing over to the next team a real opportunity for a brighter future in the Middle East,” he said. “I hope they accept him.”

After several months of stalling, the negotiations in Doha, the capital of Qatar, went into high gear in recent days, accelerated by the upcoming inauguration of Mr. Trump. American officials of both the outgoing and new administrations drove the latest efforts to reach an agreementwith Qatar and Egypt acting as intermediaries between Hamas and Israel.

The ceasefire would have several phases, the first of which would last six weeks. During that time, said Mr. al-Thani, Israeli forces in Gaza will withdraw to the east, away from populated areas, and about 33 hostages will be freed. In return, Palestinian prisoners held in Israel would be freed.

Among the 33 hostages who will be released in the first phase are women and children, men over 50 years old and sick and wounded people. It is still unclear how many of that group are alive, but Israeli officials estimate that most are.

During the first phase, 600 trucks carrying desperately needed humanitarian aid would enter Gaza daily. And Gazans driven from their homes will be able to return to the north, where the Israeli invasion began.

Hundreds of thousands of Palestinians in southern Gaza have been living in tents, makeshift shelters, rented houses and relatives’ apartments for more than a year. Many of those planning to return north will likely find their homes and neighborhoods destroyed.

By the 16th, negotiations will begin on the second phase of the deal – which will also last six weeks – focusing on further exchanges of hostages and Palestinian prisoners.

The cease-fire agreement still has to pass through Israel’s government, where some of the far-right lawmakers on whom Prime Minister Benjamin Netanyahu depends to stay in power have openly opposed the deal.

Amid news that a cease-fire agreement may be close, one far-right member of the coalition, Itamar Ben-Gvir, issued video statement urging others to join forces and undo any agreement by leaving Netanyahu’s government.

Another far-right cabinet member, Finance Minister Bezalel Smotrich, called the deal “bad and dangerous for Israel’s national security” and said he was absolutely opposed to it. But he did not explicitly threaten to leave the government.

Mr. Netanyahu’s critics, including many of the families of the hostages, have often accused him of sabotaging previous efforts to reach a deal to preserve his coalition, the most right-wing and religiously conservative in Israel’s history.

On Wednesday, Foreign Minister Gideon Saar said he believed a majority would sign the deal in a cabinet vote. “Leadership is deciding between a bad decision and a very bad decision,” Mr. Saar said, adding of the hostages: “If we delay the decision, we don’t know how many will survive.”

Isaac Herzog, Israel’s president, urged the government to approve the deal. “There is no greater moral, human, Jewish or Israeli obligation than to bring our sons and daughters back to us – whether to recover at home or to be laid to rest,” he said.

On Wednesday, in the absence of a ceasefire, the Gaza Civil Defense reported continued Israeli airstrikes across the enclave, including one on a residential building in northern Gaza City that it said resulted in two deaths.

Over the past year, the fighting in Gaza, along with the lawlessness that has spread since the invasion, have posed major obstacles to aid distribution. On Wednesday, as aid groups prepared to enter the stricken enclave, they made it clear that it still won’t be easy – even with a ceasefire.

“This is a moment of hope and opportunity,” said Tom Fletcher, United Nations Under-Secretary-General for Humanitarian Affairs. “But we should have no illusions about how difficult it will continue to be to get support for survivors.”

They contributed to the report Error Yazbek, Abu Bakr Bashir, Jonathan Reiss, Rawan Sheikh Ahmad, Ismael To and Ephrat Livni.