The departure of Gantz's centrist party will not pose an immediate threat to the government. But it could have a serious impact nonetheless, leaving Netanyahu reliant on hardliners, with no end in sight to the Gaza war and a possible escalation in fighting with Lebanese Hezbollah.
Last month, Gantz presented Netanyahu with a June 8 deadline to come up with a clear day-after strategy for Gaza, where Israel has been pressing a devastating military offensive against the ruling Palestinian militant group Hamas. Netanyahu brushed off the ultimatum soon after it was given.
On Sunday, Gantz said politics was clouding fateful strategic decisions in Netanyahu's cabinet. Quitting while hostages were still in Gaza and soldiers fighting there was an excruciating decision, he said.
"Netanyahu is preventing us from advancing toward true victory," Gantz said in a televised news conference. "That is why we are leaving the emergency government today, with a heavy heart but with full confidence."
Netanyahu responded in a social media post, telling Gantz it was no time to abandon the battlefront.
With Gantz gone, Netanyahu would lose the backing of a centrist bloc that has helped broaden support for the government in Israel and abroad, at a time of increasing diplomatic and domestic pressure eight months into the Gaza war.
While his coalition remains in control of 64 of parliament's 120 seats, Netanyahu will now have to rely more heavily on the political backing of ultra-nationalist parties, whose leaders angered Washington even before the war and who have since called for a complete Israeli occupation of Gaza.
This would likely increase strains already apparent in relations with the United States and intensify public pressure at home, with the months-long military campaign still not achieving its stated goals - the destruction of Hamas and the return of more than 100 remaining hostages held in Gaza.
Polls have shown Gantz, a former army commander and defence minister, to be the most formidable political rival to Netanyahu, whose image as a security hawk was shattered by the October 07, 2023 attack by Hamas on Israel.
Warning that the conflict in Gaza could take years, he urged Netanyahu to agree on an election date in the autumn, to avoid further political infighting at a time of national emergency.
Gantz joined a unity government soon after October 07 as part of Netanyahu's inner war cabinet where he, Netanyahu and Defence Minister Yoav Gallant alone had votes.
On Sunday, Gantz described Gallant, who has sparred with Netanyahu and some ultra-nationalists ministers, as a brave leader and called on him 'to do the right thing,' though he did not elaborate on what that meant.
Far-right National Security Minister Itamar Ben-Gvir demanded Gantz's now vacant seat at the war cabinet soon after the resignation was announced.
Finance Minister Bezalel Smotrich said in a statement Gantz was giving Israel's enemies what they want.
Asked whether he was worried about his departure impacting Israel's standing abroad, Gantz said Gallant and Netanyahu both know "what should be done."
"Hopefully they will stick to what should be done and then it will be okay," he said.
