Haniyeh, a former deputy chief, will replace Qatar-based veteran Khaled Meshaal, who steps down at the end of his term limit just as Hamas appeared to have softened its stance towards Israel in a new policy document last week.
The group maintains a sizeable armed wing in the Gaza Strip since seizing the coastal territory in 2007 from the rival Fatah party, which is based in the West Bank, and has fought three wars with Israel.
Hamas is listed as a terrorist organisation by the United States and European Union. Some political analysts and U.N. officials believe a more regular engagement with Hamas’s political wing could help moderate the group’s overall position.
Hamas last week dropped its longstanding call for Israel’s destruction and severed ties with the Muslim Brotherhood in a policy shakeup announced at its main overseas office in the Qatari capital.
The move, dismissed by Israel, appeared aimed at improving ties with Gulf states and Egypt as Abbas visited new U.S. President Donald Trump in Washington, who expressed interest in renewing Israeli-Palesitinian peace efforts.