"From here, we announce with other (factional) leaders, that we are ending the division," senior Fatah official Jibril Rajoub told a crowd of about 1,000 who gathered for a demonstration in Ramallah, the West Bank's political capital.
Among those present at the rally were top members of Hamas's leadership in the West Bank as well as senior officials from its smaller rival Islamic Jihad, the AFP correspondent said.
Ramallah's Manara Square was a sea of Palestinian flags as the crowd chanted "Unity!" and "Hit, hit Tel Aviv" in an appeal to Hamas militants who have fired at least five rockets at the coastal city since Thursday.
"Whoever speaks about the division after today is a criminal," top Hamas leader Mahmud al-Ramahi told the crowd.
Fatah and Hamas, the two main Palestinian national factions, have been locked in a bitter dispute for years.
But the ongoing bloodshed in the Hamas-run Gaza Strip, where Israel was on Monday pressing a sixth day of a major aerial campaign which has so far killed 91 Palestinians, appears to have prompted a rethink of traditional rivalries.
Gaza's Hamas-run government has long been at loggerheads with the rival Fatah-dominated Palestinian Authority in the West Bank and a unity deal struck between the two in April 2011, fell apart as the two bickered over the formation of a caretaker cabinet.