TEL AVIV—Hamas leader Khaled Meshaal visited Gaza for the first time to celebrate the Palestinian militant group's 25th anniversary, underscoring Hamas's growing acceptance in the region two weeks after it reached a cease-fire with Israel.

Mr. Meshaal, who knelt and kissed the ground after crossing the border from Egypt on Friday, was the target of an botched Israeli assassination attempt 15 years ago during Israeli Prime Minister Benjamin Netanyahu's first term. His arrival to the Palestinian territories...