He was a high-profile political leader and spokesman regularly interviewed in the US media. A skilled negotiator who knew the value of compromise, he was committed to working with the Palestinian Authority.
Abu Shanab was not a military commander.
His death strikes a blow at the heart of the peace process between Israel and Palestine, and is likely to ignite a region already on the brink.
Born in 1955 in the village of al-Jeyeh, near the southern city of Ashqelon, Abu Shanab was married and the father of 11 children. The youngest is less than a year old.
"The truce is dead. We're now back to the vicious cycle of violence"
Ali al-Jirbawi, Professor of International Relations, Bir-Zeit University, West Bank
"It will be hard to find another Palestinian interlocutor.Who would wish to pick up such a poisoned chalice?"
Neil Partick, Middle East analyst, The Economist, London
"In a paradoxical sense, this gets Abbas off the hook. He has been under pressure to do what he was unable to do (rein in the armed groups). Now he has a politically good pretext not to do it"
Mark Heller, Principal Research Associate, Israel's Jaffee Centre for Strategic Studies
"The truce was never alive, nor was the road map. The truce is a hudna' (ceasefire) - it was never agreed between two sides. The terms were set by the Palestinians"
Gerald Steinberg, head of Conflict Management Programme, Israel's Bar-Ilan University
"His assassination is a big loss to Hamas as a movement, but the only consolation is that Israel will pay a heavy price in blood for killing him"
He studied engineering in Egypt and received a master's degree in the United States.
He spent 10 years in Israeli prisons for leading Hamas’ political wing during the first Intifada, following the arrest of Sheikh Ahmad Yasin, the founder and spiritual leader of Hamas.
Until his untimely death, he worked as an engineering lecturer at Gaza’s Islamic University. He was also a key union figure, and had served as the head of the engineers union twice since being freed from Israeli prisons.
Responding to the news of his assassination, Sheikh Ahmad Yasin told Aljazeera that a “horrible, unprecedented crime” had been committed by Israel.
“The assassination of a political leader is a violation of all norms and a sabotage of all previous agreements,” he said.
Ismail Haniya, another Hamas leader, said that Israel’s killing of Abu Shanab signalled the Jewish state’s termination of a shaky truce in place since 29 June but repeatedly violated by Israeli incursions into Palestinian territory.
“Hamas’ retaliation for the operation will take the form of deeds, not words,” he said.
Israel said the high-profile, US-educated engineer was a member of Hamas's brain trust, which it accused of planning bomb attacks and strengthening a "terrorist infrastructure" during the ceasefire.
"Abu Shanab supported ... the continuation of Hamas' armed struggle and suicide attacks against Israeli targets," an Israeli security source said.
Abu Shanab took part in several rounds of dialogue with reformist Palestinian President Mahmud Abbas on the truce underpinning a US-backed Middle East peace plan.
The attack was condemned by Abbas, who is under international pressure to crack down on armed groups.
Hamas and another militant group, Islamic Jihad, declared the ceasefire dead after Abu Shanab was killed in the attack in Gaza City.
"As late as yesterday, he spoke about the necessity to continue the dialogue with the Palestinian Authority," a Hamas official said. "He was a man of great wisdom, who spared no effort to push towards a Palestinian unity."
In April last year, Ismail Abu Shanab showed his willingness to bring Hamas and Israel to a settlement. He declared that if Israel agreed to the so-called Saudi plan, which called for the Jewish state to return to its pre-1967 borders in return for "normal relations" with Arab nations, Hamas would "cease all military activities."
"That would be satisfactory for all Palestinian military groups to stop and build our state, to be busy in our own affairs, and have good neighbour relations with Israelis," he said.
His vision is in severe jeopardy, now that he is dead.