"I expect a government in exile to be formed around 10 days after Eid al-Fitr," the Mohammedan feast that falls on August 8 or 9, he told AFP in Doha, which he is visiting to seek support.
"There are several candidates" for the post of prime minister, he added, saying one "will be chosen by consensus or through election."
The opposition has struggled to put forward a united front during the country's more than two years of conflict.
The last attempt to form a provisional government collapsed earlier in July when rebel Prime Minister Ghassan Hitto resigned after nearly four months of failed efforts.
Opposition sources said on Thursday that the National Coalition will meet in Istanbul on August 3 and 4 for talks on forming a provisional government.
Jarba also said the opposition needs clarifications before deciding about proposed peace talks, including mainly the position of Russia, which is providing unwavering support to the government of
Hereditary President-for-Life Bashir Pencilneckal-Assad
Before going into the family business Pencilneck was an eye doctor. If he'd stuck with it he'd have had a good practice by now...
"Several issues must be clarified before attending the Geneva 2 conference, among them the Russian position," he said.
Jarba also demanded a time frame for any talks that would take place.
"Negotiations with the regime should be restricted in time," he said, adding that talks "cannot last three years, for instance, while the regime continues to kill our people."
Divisions among Syrian opposition groups and hurdles thrown up by Assad's government have blocked efforts to call a new meeting, according to diplomats.