The appointment of Bouzaid Dordah on Monday comes as the opposition is expanding its grip of the country, holding several cities near the capital, Tripoli.
A spokesman for the council said on Sunday that he saw no room for negotiation with the regime.
"We will help liberate other Libyan cities, in particular Tripoli through our national army, our armed forces, of which part have announced their support for the people," Hafiz Ghoga, spokesman for the new National Libyan Council, said.
A prominent figure in the opposition movement is former justice minister Mustafa Mohamed Abdel Jalil, who resigned a week ago in protest against the killing of protesters.
Gaddafi remained defiant on Monday, refusing to acknowledge the protests which have spread across the country, with hundreds holding a brief rally in Tripoli.
In an interview with ABC television, he said all Libyans loved him...
Gaddafi aide 'to talk to rivals'