The conference in the occupied West Bank town of Bethlehem is Fatah's first congress for 20 years and the first on Palestinian soil.
'Wind of change'
The conference, originally scheduled to last for three days, is seen as an opportunity for Fatah to restructure and rejuvenate itself.
There are hopes among the delegates that some of the old guard, often accused of corruption, will make way for younger members of the party, founded by Yasser Arafat, the iconic Palestinian leader, in the late 1950s.
"At the end of the congress, Fatah will have new leadership where the young generation will play a key role," Nabil Shaath, a prominent Fatah member, wrote on the congress's website.
"This will reinvigorate the movement and strengthen its legitimacy."
But on Saturday voting for the movement's governing bodies was postponed for a second time.
Delegates are now set to vote for members of the 21-strong Central Committee and the 120-member Revolutionary Council on Sunday morning.
Among those seen as leading candidates are Marwan Barghouthi, the party's West Bank secretary-general who is currently being held in an Israeli prison, Jibril Rajub, a former preventive security chief, and Mohammed Dahlan, once Fatah's security chief in the Gaza Strip.
"A strong wind of change is blowing over the congress. In my view, at least half the current members of the Central Committee and the Revolutionary Council will be replaced," one delegate said.
All Fatah party members will be allowed to vote in person or by proxy, including dozens who Hamas have prevented from leaving the Gaza Strip to attend the conference, Shaath said.
Longstanding tensions between Hamas and Fatah boiled over in June 2007 when Hamas seized control of Gaza, confining Abbas's power base to the Israeli-occupied West Bank.
Hamas, which now controls the Gaza Strip, refused to allow Gaza-based Fatah delegates to attend the conference unless Fatah released Hamas activists held in the West Bank.