Earlier on Tuesday, Israeli forces issued new evacuation orders in the north of the Gaza Strip and carried out military strikes which Palestinian medics and media said had killed at least 35 people since Monday night.
The prime minister named Gideon Saar as the new foreign minister, Netanyahu's office said in a statement.
Gallant and Netanyahu, both in the right-wing Likud party, have clashed for months over the objectives of Israel's 13-month-old war in Gaza against Palestinian militant group Hamas.
Netanyahu said Gallant has made statements that "contradict the decisions of the government and the decisions of the cabinet".
Protests broke out in Tel Aviv and elsewhere against the Yoav Gallant's sacking. (AP PHOTO)
In response, Gallant said: "The security of the state of Israel always was and will always remain my life's mission."
Katz said on social media platform X that he would approach his new role "with a sense of mission and holy fear for the security of the State of Israel and its citizens."
Reports appeared in September that Netanyahu, under pressure from far-right coalition partners, was considering firing Gallant.
Protests erupted in Tel Aviv and other parts of Israel after Gallant's firing.
"Firing Gallant in the middle of a war is an act of madness," said Israeli opposition leader Yair Lapid on X.
In Washington, a spokesperson for the White House National Security Council said Gallant had been an important partner and that it would continue working collaboratively with Katz.
France's foreign minister will travel to Israel and the Palestinian territories on Wednesday, a day after US elections, to press Israel to engage diplomatically to end the conflicts in Gaza and Lebanon.
New defence minister Israel Katz vowed to approach his role with "a sense of holy fear for Israel". (EPA PHOTO)
Acting UN aid chief Joyce Msuya said on X that Israeli military ground operations in northern Gaza had left Palestinians "without the essentials to survive, forced them to flee for safety multiple times, and cut off their escape and supply routes".
"These atrocities must stop," she said.
An air strike late on Monday damaged two houses in the town of Beit Lahiya, killing at least 20 people, the Palestinian official news agency WAFA and Hamas media said.
Ten were killed in central areas of the Palestinian enclave - six in separate air strikes on Gaza City and the town of Deir Al-Balah, and four in the town of Al-Zawayda around midnight on Monday, medics and health officials said.
At least five others were killed in an Israeli strike on a house in Jabalia north of Gaza City, medics said later on Tuesday.
The Israeli military said, without giving details, that its forces had "eliminated terrorists" in the central Gaza Strip and Jabalia area.
Israeli troops had also found weapons and explosives over the past day in the southern Rafah area, where "terrorist infrastructure sites" had been eliminated, it said.
Much of Gaza is in ruins and many of the population have been displaced and reliant on aid. (AP PHOTO)
Later on Tuesday, Israeli planes dropped leaflets over Beit Lahiya ordering residents who had not yet left their homes and shelters housing displaced families to quit the town completely.
Palestinians said the new attacks and Israeli orders for people to evacuate were aimed at emptying areas to create buffer zones.
Israel says the evacuations are meant to keep civilians out of harm's way as its troops battle Hamas fighters.
Hundreds of Palestinian gunmen have been killed or captured in the Jabalia area in the past month, the military says.
More than 43,300 Palestinians have been killed in more than a year of war in Gaza, health authorities in Gaza say, and much of the territory has been reduced to ruins.
The war began after Hamas-led militants attacked Israel on October 7, 2023, killing about 1200 people and taking 251 hostages to Gaza, according to Israeli tallies.
Announcing plans for a rare transfer of patients out of Gaza, a World Health Organisation official said more than 100 people would be evacuated from Gaza on Wednesday, including children suffering from trauma injuries and chronic diseases.
with Reuters
