Mr Brahimi challenged those in the conflict to work together to pave the way for democratic elections and sideline President Bashar al-Assad.
His proposal received strong backing from Sergei Lavrov, the Russian foreign minister, who said negotiations were the only way to end the fighting.
"The alternative to a peaceful solution is bloody chaos. The longer it continues, the greater its scale – and the worse things get for all," he said.
After five days of negotiations with the regime in Damascus, Mr Brahimi claimed to have the outline of a power-sharing pact, but his proposals were instantly rejected by the main opposition council.
It has been angered by the suggestion that Mr Assad could stay on as a figurehead despite the deaths of 45,000 people in the fighting.
The Christmas mission by Mr Brahimi and a "softening" of Russia's support for Mr Assad's regime has lifted hopes for a diplomatic end to civil war.
Mr Brahimi said the regime must make previously unthinkable concessions to the leaders of the 21-month uprising.
"Change should not be cosmetic – the Syrian people need and require real change, and everyone understands what that means," said Mr Brahimi, the joint UN- Arab League envoy.
"We need to form a government with all powers... which assumes power during a period of transition. That transition period will end with elections."
Speaking before he prepared to fly to Moscow today, Mr Brahimi warned, however, that there must not be a "collapse of the state or the state's institutions" during any power-sharing period.
Yasser Tabbara, a spokesman for the Syria Opposition Coalition, said the terms outlined by the envoy were unacceptable.
"It has been the position of the coalition that we need to find a quick solution on the issue of Bashar al-Assad stepping down," he said.
"The priority of the coalition is to preserve lives and finish this with the least casualties. The plans proposed by Mr Brahimi are out of touch with reality. The plan takes us back months and months, if not years."
Moscow has engaged in a flurry of diplomatic activity to promote power sharing and its view that there will be no military solution to the conflict. (© Daily Telegraph, London)