Azzam al-Hayya, son of Khalil al-Hayya, succumbed to his wounds on Thursday after being struck in an Israeli attack on Wednesday night, senior Hamas official Basim Naim said.
He is the fourth son of Hamas' exiled Gazan chief to have been killed in Israeli attacks.
The Israeli military did not respond to a request for comment.
Later on Thursday, health officials and the Hamas-run interior ministry said at least three police officers were killed and other people, including one policeman, were wounded when an Israeli air strike targeted a police post in western Gaza City.
Reuters has reported that Israel has intensified its attacks on the Hamas-run police force in the Gaza Strip, which the militant group has used to reinforce its hold in the areas it controls in the strip.
Hayya, who has seven children, has survived multiple Israeli attempts to kill him. An Israeli strike in Doha in 2025 targeting Hamas leadership killed another son, though Hayya survived. Two other sons were killed in past Israeli attempts on his life, in Gaza strikes in 2008 and 2014.
Speaking to Al Jazeera after the attack on Wednesday night, before his son's death was announced, Hayya accused Israel of trying to undermine mediators' efforts to push ahead with US President Donald Trump's Gaza plan, overseen by his Board of Peace.
"These Zionist attacks and violations clearly indicate that the occupation does not want to abide by a ceasefire or by the first phase," Hayya said.
Chanting "Allahu akbar", or "God is Greatest", dozens of Palestinians rallied in Gaza at the funeral of Hayya, the son, and held special prayers before walking him to burial. Women relatives paid respects to the white-shrouded body.
The group's Gaza spokesperson, Hazem Qassem, said the killing of the Hamas leader's son was a failed attempt by Israel to influence the negotiating team and win political concessions.
"We say that this repeated policy of targeting the leaders and the sons of leaders will not succeed in extorting a political position from our Palestinian people, nor the Hamas leadership, nor its negotiating delegation," Qassem told Reuters.
The violence comes as leaders of Hamas and other Palestinian factions held talks with regional mediators and the Board of Peace's lead envoy, Nickolay Mladenov, this week in Cairo, to push Trump's Gaza plan into its second phase, officials said.
The plan, which Israel and Hamas agreed to in October, involves Israeli troops withdrawing from Gaza and reconstruction starting as Hamas lays down its weapons.
At least 830 Palestinians have been killed since the ceasefire deal took effect, according to local medics, while Israel says militants have killed four of its soldiers over the same period.
Israel says its strikes are aimed at thwarting attempts by Hamas and other Palestinian militants to stage attacks against its forces.
