National Transitional Council (NTC) chief Mustafa Abdel Jalil will pass the reins on Wednesday to the oldest member of the 200-seat legislative assembly elected on 7 July at a late-evening ceremony.
The ceremony was due to get under way at 2100 GMT.
NTC member Mokhtar Jadal said both men will speak before the council is dissolved.
A conference room has been arranged in an upscale hotel in the Libyan capital as a makeshift venue for the assembly, which is due to begin its work after a week, according to the official LANA news agency.
The authorities have put in place tight security measures for the ceremony, in view of the ongoing violence in Benghazi and in the capital, where a car exploded during a marketplace gunbattle on Saturday.
The interior ministry said it had cordoned off the hotel and that "all the roads near or leading to the conference will be closed" between 1700 and 0100 GMT.
Representatives of civil society groups and diplomatic missions in Libya, as well as NTC and government officials are due to attend.
The General National Congress, the outcome of last month's ballot, will be tasked with choosing a new interim government to take over from the NTC, and will steer the country until fresh elections can be held, based on a new constitution, to be drafted by a constituent authority of 60 members.
Assembly members, who have been converging on Tripoli since Sunday, held an informal meeting on Monday and agreed on the need to select a head of the GNC and two deputy chiefs within a week, according to Salah Jawooda, an independent member from the eastern city of Benghazi.
A committee will also be chosen to write its internal procedural rules.
Libyans elected a legislative assembly of party and independent representatives last month, in their first free vote since a popular uprising last year escalated into a civil war that ousted the now-slain dictator.
Of the 200 assembly members, the lion's share of seats has been set aside for individual candidates whose loyalties and ideologies remain unclear but who are being wooed by various blocs.
Out of the parties, which hold 80 of the 200 seats, the liberal coalition of 2011 wartime premier Mahmud Jibril performed best, securing 39 seats on its own.
Jibril's National Forces Alliance also counts on the support of a centrist party led by Ali Tarhuni, who held several key posts during last year's revolt. It obtained two seats in the congress.
The Justice and Construction Party, launched by Libya's Muslim Brotherhood, came second with 17 seats. But its leader, Mohammed Sawan, says the party can even the score by bringing independent candidates to its side.
Whether two or three major forces emerge in the congress, decisions in the assembly require a two-thirds majority to pass, making cooperation necessary to avoid gridlock in a delicate transition.
Jawooda dismissed suggestions that a new government could be in place before the Eid al-Fitr festival that follows Ramadan, which is due to conclude in around 10 days.
"It is premature to discuss this now," he told AFP.
The NTC was the political arm of the rebellion that toppled Gaddafi, and officially assumed power after the regime was overthrown.
It presided over a transition period marked by high levels of insecurity, after its failure to integrate or disarm the ex-rebel militias who helped oust Gaddafi.