Hamas says it is to join the Palestine Liberation Organisation.
After a meeting in Cairo with the PLO, Hamas said it had reached an agreement on its membership with Fatah.
The two factions have been rivals for years. Hamas has governed Gaza since 2006 and Fatah is in power in the West Bank.
Previous attempts to reconcile have failed. The BBC reports their reconciliation will complicate peace moves in the Middle East.
Hamas refuses to renounce violence or recognize Israel's right to exist.