The meeting in Marrakesh coincides with a rapidly deteriorating refugee situation as winter sets in, and gains in the battlefield by a key rebel group suspected of links to Al-Qaeda.
Headlining the agenda for Arab and Western states are two key issues, namely the political transition after Assad's eventual fall and mobilising humanitarian aid.
With the total death toll from the conflict now topping 42,000, according to a monitoring group, the UN refugee agency said on Tuesday that the number of Syrian refugees who had fled to neighbouring countries and north Africa had now passed half a million.
But in a major boost for the newly-formed opposition coalition, and the most significant US intervention yet in the brutal civil war, President Barack Obama on Tuesday endorsed the group as "the legitimate representative" of the Syrian people.
"We have made a decision that the Syrian opposition coalition is now inclusive enough, is reflective and representative enough of the Syrian population, that we consider them the legitimate representative of the Syrian people," Obama told ABC News in an interview, on the eve of the Morocco meeting.
Under international pressure to unite, after struggling for months to do so, the Syrian opposition agreed in Doha on November 11 to establish the national coalition and group the various rebel forces under a supreme military council.
Obama's announcement follows a similar move by the European Union on Monday, after EU foreign ministers met the coalition's leader, Ahmed Moaz al-Khatib.
Earlier, Western diplomats and members of the newly-formed rebel National Coalition had expressed confidence that the opposition group would consolidate its international backing as a viable alternative to President Assad's beleaguered regime.
"It is our goal that, after the European Union, now the 130 states in the Friends of Syria group will send a message of recognition to the national coalition of the Syrian opposition," German Foreign Minister Guido Westerwelle said on Tuesday, before flying to Morocco.