LONDON — A ceasefire deal has been reached between Israel and Hamas, Qatari officials announced Wednesday, pausing more than 15 months of vicious fighting in Gaza, during which time the Middle East has been “fundamentally changed,” in the words of President Joe Biden.

As talks aimed at ending the Israel-Hamas conflict inched forward in Qatar over the last year, a deal had, at times, appeared close, but each time, one or both sides pulled back from the negotiating table before it could be finalized.

There had been disputes in the high-stakes talks over the terms, which have always included the return by Hamas of the remaining hostages, and the military withdrawal by Israel from the Gaza Strip.

The deal also follows the high-profile assassinations last year of Hamas leaders Ismail Haniyeh and Yahya Sinwar — with Sinwar being one of the key architects of the Oct. 7, 2023, terror attack on Israel — as well as Hezbollah leader Hassan Nasrallah. Israel has claimed responsibility for their deaths.

Throughout it all, the brutal war in Gaza continued in the foreground, its near-daily death toll overshadowing efforts to stop it.

But on Wednesday, officials announced that Israel and Hamas had finally reached a deal mediators hope will scale back and eventually end the war.

For more than a year, the two sides have been locked in a fierce and brutal conflict in Gaza, a bloody attritional contest jumpstarted by Hamas’ deadly surprise attack in southern Israel. More than 1,200 people were killed and another 253 were taken hostage, according to Israeli authorities.

In over a year of war between Israel and Hamas, more than 46,000 people have been killed in Gaza and almost 110,000 injured, according to the Hamas-run Gaza Health Ministry. That figure does not distinguish between civilians and combatants. However, more than 14,000 children and 8,000 women have been killed, according to the health ministry. The Israel Defense Forces (IDF) said they have killed more than 15,000 combatants throughout the course of the war.

After the new year began, there seemed to be a sea change in sentiment. On Monday, President Biden announced mediators had reached “the brink” of a deal.

The president and his top diplomats, including Secretary of State Antony Blinken, had sought closure during his term in office. They said they wanted the deal to be reached before Jan. 20, when President-elect Donald Trump again takes office.

Biden laid the deal’s foundation in May 2024

A source told ABC News in February 2024 that Israeli officials had agreed to the terms of a deal, which would have seen 40 hostages released. Officials from Qatar, Egypt, Israel and the United States had met in Paris to work out the details, which included the release of some Palestinians imprisoned by Israel, the source said at the time.

But that effort seemed to stall. By May, the talks were again at a “critical” stage, White House spokesperson John Kirby said at the time. Hamas had been said to agree to a deal but by the next month, the U.S. said the militant group was reluctant to sign an agreement.

Then in July, talks were stalled when Hamas leader Ismail Haniyeh, a key facilitator in the talks, was killed in Iran. The group’s militant leader, Yahya Sinwar, was killed in Gaza in October, throwing fresh uncertainty into the process.

Throughout, the talks in Doha had been mediated by the Qataris, including Emir Sheikh Tamim bin Hamad Al Thani, and the Egyptians, with help from the U.S. and others.

Biden and the Qatari leader spoke on Sunday, according to a readout from the White House. They both “emphasized the urgent need for a deal” to bring relief to the hostage families.

“We remain hopeful that each step brings us closer to bringing everyone home,” the Hostage Families’ Forum said on Tuesday morning.

A deal would also allow for a much-needed “surge” of humanitarian aid into Gaza, Biden had said.

The agreement that was finally approaching was based on what Biden had laid out in May 2024, an arrangement that had been endorsed unanimously by the United Nations Security Council at the time, the White House said.

“Today we are at a point that is closest to reaching an agreement on Gaza,” a spokesperson for the Qatari Foreign Ministry said on Tuesday.

As negotiations continued, sticking points became public

Previous humanitarian pauses repeatedly raised hopes of a lasting ceasefire, but the fighting always resumed.

In November 2023, a brief ceasefire was reached. During that truce, more than 100 hostages taken during the Oct. 7 attacks were freed in exchange for the release of 240 Palestinian prisoners and detainees.

Hamas accused Israel of refusing to extend the ceasefire, but Israel and the U.S. said it was Hamas that brought the pause to a close by firing rockets into the Israeli city of Sderot.

Talks aimed at achieving a more lasting peace fell apart but eventually resumed, although Hamas repeatedly claimed Israeli Prime Minister Benjamin Netanyahu was torpedoing negotiations in a bid to shore up his domestic political position, heading off legal pressure and opposition calls for new elections. The militant group also cited repeated killings of Hamas leaders, as well as Iranian and Hezbollah officials in Lebanon, Iran and Syria.

Netanyahu, meanwhile, said the continued deaths of hostages in Hamas captivity indicated the group had no interest in peace. Publicly, the prime minister and most of his top officials remained committed to their goal of “eradicating” Hamas in its entirety.

The Biden administration’s frustration with its inability to bring the two sides to a deal was often evident, particularly as the death toll in Gaza and elsewhere continued to grow.

In September — shortly after Israel remotely detonated explosives hidden in Hezbollah pagers and walkie-talkies across Lebanon — Blinken said mediation efforts had been undermined “time and again.”

Every time talks made progress, Blinken said, “we’ve seen an event that makes the process more difficult, might derail it.”

A final push from two administrations

Trump’s November reelection victory gave fresh impetus to the stalled negotiations, with Trump and his incoming Middle East envoy, Steve Witkoff, making clear the incoming president’s desire for a deal before his inauguration on Jan. 20.

Trump threatened “all hell will break out in the Middle East” if the remaining Gaza hostages were not freed by the time he returned to office. “It will not be good for Hamas, and it will not be good, frankly, for anyone,” he said.

Witkoff repeatedly traveled to the region in pursuit of a deal, telling reporters that he and Biden’s envoy, Brett McGurk, were “collaborative” in their push for an accord.

The Biden administration, Blinken said, “very much” hoped to get the agreement “over the finish line in the next two weeks, the time we have remaining.”

Negotiators returned to Doha in early January, with high-level representatives — among them Mossad chief David Barnea — joining talks later as they progressed toward a conclusion.

In the closing days of talks, both Israeli and Hamas officials signaled their readiness to make a deal, though far-right elements of Netanyahu’s government again threatened to collapse the ruling coalition in protest of a ceasefire.

ABC News’ Will Gretsky, Joe Simonetti and Shannon K. Kingston contributed to this report.