The group said Ramadan Abdullah Shalah, 62, died of an illness.
"We have been witnessing the struggle of the Islamic Jihad movement since its establishment, and we remember his leadership and national stance with honor and dignity,” it said in a statement and added that Shalah always protected his Arab and Islamic identity by supporting Palestinian resistance.
Palestinian President Mahmoud Abbas issued a condolence message, according to the Palestinian official news agency, WAFA.
"By losing Shalah we lost a great national man," Abbas said.
Shalah was born in Gaza in 1958 and became the head of the movement in 1995 after the assassination of Fathi Shaqaqi.
Ziad al-Nakhala was chosen to lead the Palestinian Islamic Jihad Movement in 2018 because of Shalah’s illness.