Brahimi wants the temporary truce to be in place during the Islamic Id al-Adha feast that begins Friday, The New York Times reported.
The envoy, who represents both the United Nations and Arab League, said in Cairo Syria was preparing to announce the cease-fire and most rebel factions he had contacted said they would respect it as well.
Syrian state television said an announcement about the truce would be made Thursday.
How the truce will be enforced is uncertain. U.N. observers were pulled out last year and it isn't likely a peacekeeping force could be assembled in 48 hours.
Rebel leaders said in various statements they doubted the cease-fire would hold. They said Syria would agree to a cease-fire only to gain time to regroup against rebel forces. Commanders noted government forces were shelling rebel bases and civilians in cities around the country.
Some commanders said they would honor the cease-fire if other conditions were met, such as releasing prisoners held as rebels and lifting sieges around major cities.
Meanwhile, rebels and government forces blamed one another for what the government called a "massacre" in Douma, a Damascus suburb, CNN reported.
While opposition forces said government troops were to blame, Syria's state-run media reported "terrorist armed groups committed a heinous massacre," using knives to kill nine men, one woman and three children.
In Jordan, Health Minister Abdullatif Wreikat said providing healthcare to Syrian refugees has depleted resources and placed great pressure on Jordanian hospitals and clinics, Jordan's official Petra news agency said. He said Jordan, home to more than 200,000 refugees, needs more aid.