The surprise deal, announced last week, comes after 18 months of failed talks and envisions the formation of an interim government of independents that will prepare the way for presidential and legislative elections within a year.
It largely maintains the status quo, leaving Hamas in control of the Gaza Strip and the Fatah-dominated Palestinian Authority ruling the West Bank.
And it does not affect the mechanisms for negotiations with Israel, though peace talks have been on hold for months now and do not look likely to resume in the near future.
The deal will be signed by Fatah's Azzam al-Ahmad and Mussa Abu Marzuk, the number two in Hamas's political bureau, who hashed out the details of the agreement with help from Egyptian officials.
It will also be signed by a variety of Palestinian factions, including Islamic Jihad, the Popular Front for the Liberation of Palestine, the Democratic Front for the Liberation of Palestine and the Palestinian People's Party.
A ceremony to mark the signing is scheduled for Wednesday, and will be attended by Hamas chief Khaled Meshaal, who flew in Sunday from Damascus, and Palestinian president Mahmud Abbas, who is due to arrive on Tuesday.
Abbas last met with Meshaal at the end of April 2007, just six weeks before Hamas took over the Gaza Strip, forcibly ousting Fatah after a bloody confrontation that dramatically worsened the bitter split between the two movements.
The ceremony, at which Abbas will speak, will also be attended by Egyptian Foreign Minister Nabil al-Arabi, Egyptian intelligence chief General Murad Muwafi and Arab League head Amr Mussa.
Palestinian sources said former US president Jimmy Carter had also been invited.
Abbas and Meshaal are scheduled to meet several times between Tuesday and Thursday, and will also hold talks with Egyptian officials about ways to implement the agreement.
Among the first tasks to be tackled is the establishment of a higher security council tasked with examining ways to integrate Hamas and Fatah's rival security forces and creating a "professional" security service.
The accord also calls for the creation of an electoral tribunal and for the release of a number prisoners held by the rival movement in jails in the West Bank and Gaza.
The two parties will also have to begin work immediately on the creation of the interim government of independents.
The new cabinet will replace the two rival governments -- one in the West Bank which is headed by Salam Fayyad, an independent, and the other in Gaza which is led by Hamas premier Ismail Haniya.
The future role of Fayyad, who has won international praise, particularly from donors for his programme of institution-building, remains unclear.
Senior Hamas leader Mahmud Zahar, who participated in the negotiations that led to the Cairo agreement, told the pan-Arab Al-Hayat newspaper that the interim prime minister would be an independent from the Gaza Strip.
"The choice for head of the government will be made by consensus," he said, rejecting what he said were European calls for Fayyad to be kept in office.
"The formation of a government will be in the context of a Palestinian national reconciliation, not a Palestinian-European reconciliation," he said.
Israel has fiercely criticised the unity deal, with Prime Minister Benjamin Netanyahu even warning Abbas he "must choose between peace with Israel or peace with Hamas."
But Abbas said last week that the deal would not affect talks with Israel, which remain the remit of the Palestine Liberation Organisation which he heads.
And Hamas has said that while it has no intention of talking to Israel, it will not try to stop Fatah from doing so.