Hamas has chosen Yahya Sinwar, one of the masterminds of the deadly Oct. 7 attacks on Israel, to lead the militant group’s political wing, it announced on Tuesday, consolidating his power over Hamas as it continues to fight Israel in the Gaza Strip.

Mr. Sinwar, the leader of Hamas in Gaza since 2017, has long been considered an architect of Hamas’s military strategy there. Now, he will also replace Ismail Haniyeh, the group’s previous political leader and a key liaison in the indirect cease-fire talks with Israel. Mr. Haniyeh, who had been living in Qatar, was killed in an explosion in Iran last week that has been widely attributed to Israel.

A hard-line figure born in Gaza, Mr. Sinwar, 61, is a prime target for Israeli forces and is widely believed to be hiding out in tunnels underneath the enclave to avoid Israeli attack. Despite that, he is thought to have been dictating the group’s position in the cease-fire talks.

His selection to lead the group’s political office comes as the Middle East braces for Iran and its proxies, including Hamas, Hezbollah in Lebanon and the Houthis in Yemen, to strike Israel in response to the killings last week of Mr. Haniyeh and a senior Hezbollah commander, Fuad Shukr.

Hamas and Iran have blamed Israel for planting the bomb that killed Mr. Haniyeh in the Iranian capital, Tehran, after he attended the inauguration of the country’s new president. Israel has declined to comment on Mr. Haniyeh’s death, but U.S. officials have privately assessed that Israel was behind it.