The UN did not specify the reason for Nasser al-Kidwa's prompt departure, but said that he had indicated "his willingness to serve the United Nations in other capacities."
UN chief Ban Ki-moon thanked Kidwa for his efforts "in trying to end the bloodshed in Syria and move toward a Syrian-led transition," according to a statement by Ban's spokesman Martin Nesirky.
The nephew of former Palestinian leader Yasser Arafat, Kidwa was nominated to the job in August 2012 at the same time as Brahimi, having served his predecessor Kofi Annan as well.
Ban "expressed his appreciation" to Kidwa for his service under both Brahimi and Annan, the statement said.