Libya has had two governments and two parliaments, with the General National Congress run by rebels in the capital and the internationally-recognized administration in Tobruk.
Martin Kobler made the announcement after a ministerial meeting attended by representatives from neighboring states in Tunis on Tuesday.
Kobler said although an exact date had not been set yet, he was certain the installment would take place “in a matter of days not weeks."
Libya has been grappling with violence and political uncertainty since the oil-rich country’s former dictator Muammar Gaddafi was deposed in 2011 under NATO airstrikes and later killed by militants.
Kobler touched on Daesh inroads in the country, saying "it is urgent to stop the expansion" of the Takfiri terrorism into neighboring countries, including Tunisia.
Faez al-Sarraj, the premier in waiting, described the spread of Takfiri terrorism as a “cancer,” calling for a quick response.
He is expected to be the new prime minister under an agreement reached between rival parties last December.
Libya’s current government, however, opposed the UN-sponsored unity government just last week, dampening hopes of an improvement in the situation.
Taking advantage of the political chaos, Daesh took control of Sirte in June 2015, almost four months after the group announced its presence in the northern Libyan port city.
The capture made Sirte the first city to be ruled by the militant group outside Iraq and Syria.