Conference delegates who had struggled for days to find the unity sought by their Western and Arab backers said the new body would ensure a voice for religious and ethnic minorities and for the rebels fighting on the ground, who say they have been overlooked by exiled dissident groups.
Some details remain outstanding, including who will head the new Syrian National Coalition for Opposition and Revolutionary Forces and the final assent of some leaders not present at the conference in Qatar.
Diplomats and officials from the US and Qatar, the tiny Gulf emirate whose oil and gas wealth has helped fund the 20-month-old uprising, have been pressing the Syrian National Council, whose leaders mostly live abroad, to drop fierce objections to joining a wider body.
"An initial deal has been signed. A final formulation has been agreed and signed," said Ali Sadreddine al Bayanouni from the Muslim Brotherhood.
Delegates said there would be specific representation for women and ethnic Kurds as well as for Christians and Alawites.