The Israeli military did not offer specifics on Gal Meir Eisenkot's death, other than to indicate he was killed in fighting in northern Gaza.
"I send my support and a big hug to Gadi and his entire family on behalf of all of Israel." "We are all dedicated to continuing the fight for the sacred cause for which Gal died," Gantz said in a statement.
Netanyahu expressed his grief in a condolence message.
Israel has pledged to destroy the Palestinian Islamist militant organization Hamas after its militants killed 1,200 Israelis and hauled 240 more back to Gaza as prisoners, according to Israeli figures.
According to the health Ministry in Gaza, over 17,000 Palestinians have been dead since october 7, and 1.9 million people, or 85% of the population, have been displaced.
Hamas, recognized as a terrorist organization by the US and other Western countries, has vowed to destroy Israel.