Ismail Haniyeh, one of Hamas’s top leaders who in recent years led the Palestinian militant group’s political operations while in exile in Qatar and Turkey, was killed in Tehran on Tuesday.

Mr. Haniyeh was in Iran with other senior members of Iran’s “axis of resistance” — which includes Hamas in Gaza, Hezbollah in Lebanon and the Houthis in Yemen.

As Hamas’s political leader, he was central to the group’s high-stakes negotiations and diplomacy, including the stalled cease-fire deal negotiations with Israel. He was believed to be 62.

Mr. Haniyeh was born in 1962 in the Shati refugee camp north of Gaza City, to Palestinian parents who in 1948 had been displaced from their home in what is now Israel, in Ashkelon. He studied at schools run by the main United Nations agency for Palestinians, UNRWA, and went on to study Arabic literature at the Islamic University of Gaza.

He was arrested by the Israeli military and served several sentences in Israeli jails in the 1980s and 1990s.

The Hamas leader’s ascent to power in Gaza was aided by his mentor, the spiritual leader and a founder of Hamas, Sheik Yassin. Mr. Haniyeh served as Mr. Yassin’s personal secretary. The two were targets of an attempted Israeli assassination attempt in 2003; the next year, Mr. Yassin was killed by the Israeli military.