The deal, which the opposition said would be signed later today, would ease Yemen's entrenched President Ali Abdullah Saleh out of power within a month after a nearly 33-year rule in the impoverished state.
The GCC states' exit plan that would see a government of national unity formed, President Saleh would transfer power to his vice president and there would be an end to protests. In exchange, Mr Saleh and his top aides would be granted immunity from prosecution.
At least 180 people have been killed in clashes during protests against Mr Saleh's regime that erupted in late January, according to a toll compiled from reports by activists and medics.
Opposition official Yahya Abu Usbua said: "After American, European and Gulf efforts, there was agreement by the president on the Gulf initiative after simple changes, and the signing will be today,".
Al Arabiya television quoted an adviser to the Yemeni president as confirming the signing would take place on Wednesday.
The United States and Saudi Arabia, both targets of foiled attacks from al Qaeda's Yemen wing, are keen to see an end to Yemen's political stalemate, fearing continued chaos could give the militant group more room to operate freely. Abdullatif al Zayani, the secretary general of the Gulf Cooperation Council, has been in the capital, Sana'a, since Saturday trying to revive the GCC-brokered deal that Qatar, one of its six members, backed out of citing stalling and "lack of wisdom".
Mr Saleh, a shrewd political survivor who has outlasted previous opponents' attempts to challenge his power, indicated in April he would sign the Gulf deal, but refused to put his name to it in the final hours.
He said at the time he would only sign in his capacity as ruling party leader, not as president.
The opposition, whose coalition includes Islamists and leftists, said that among the minor modifications in the deal were changes in who would sign and in what capacity for the opposition and for the government.
"The president will sign for the government in his capacity as president of the republic and as head of the ruling party," Mr Abu Usbua said.
Protesters, frustrated that three months of street protests have failed to dislodge Mr Saleh, want the 69-year-old leader out immediately and have said they will step up their campaign by marching on government buildings, a move that brought new bloodshed last week as security forces fired to stop them.
Protesters blocked the entrance of the Red Sea port of Hudaida, Yemen's second largest port, preventing traffic from entering or leaving, protesters said. The cities of Ibb, Taiz and Hadramout were brought to a standstill as most workers complied with a strike aimed at pressuring Saleh to leave.
* Reuters and AFP