The Israeli military said that after a lengthy hunt, troops had on Wednesday “eliminated Yahya Sinwar, in an operation in the southern Gaza Strip”.
Hamas has not confirmed his death.
Netanyahu, who vowed to crush Hamas at the start of the war, hailed Sinwar’s killing, saying: “While this is not the end of the war in Gaza, it’s the beginning of the end.”
He had earlier called Sinwar’s death an “important landmark in the decline of the evil rule of Hamas”.
The chief of Hamas in Gaza at the time of the October 7 attack that sparked the war, Sinwar became the fighters group’s overall leader after the martyrdom in July of its political chief, Ismail Haniyeh.
Israel’s announcement of Sinwar’s death comes weeks after it assassinated Hezbollah chief Hassan Nasrallah in a strike in Lebanon, where the Israeli military has been at war since late September.
With Hamas already weakened more than a year into the Gaza war, Sinwar’s death dealt an immense blow to the organization.
US President Joe Biden, whose government is Israel’s top arms provider, said: “This is a good day for Israel, for the United States, and for the world.”
“There is now the opportunity for a ‘day after’ in Gaza without Hamas in power, and for a political settlement that provides a better future for Israelis and Palestinians alike.”
Hamas also seized 251 hostages during the October 7 attack and took them into Gaza. Ninety-seven remain there, including 34 who Israeli officials say are dead.
Following the attack, Netanyahu vowed to defeat Hamas and bring home all the hostages.
Israel’s retaliatory campaign has killed 42,438 people in Gaza, the majority civilians, according to data from the health ministry in the Hamas-run territory, figures which the UN considers reliable.
Israeli military chief Herzi Halevi said: “We are settling the score with Sinwar, who is responsible for that very difficult day a year ago.
Final moments
The Israeli military said Sinwar was killed in a firefight in southern Gaza’s Rafah, near the Egyptian border, while being tracked by a drone.
It released drone footage of what it said was Sinwar’s final moments, with the video showing a wounded militant throwing an object at the drone.
With the civilian toll in Gaza mounting, Israel has faced criticism over its conduct in the war, including from the United States.
In northern Gaza’s Jabalia, two hospitals said Israeli air strikes on a school sheltering displaced people killed at least 14 people.
According to a UN-backed assessment, some 345,000 Gazans face “catastrophic” levels of hunger this winter.
Nearly 100 percent of Gaza’s population now lives in poverty, the UN’s International Labour Organization said, warning that the war’s impact on Gaza “will be felt for generations to come”.