Colombia says it will allow Venezuelan aircraft into its territory to collect three hostages who could be freed by Colombian rebels in the next day or so.
Colombia ended Mr Chavez's official mediation role last month
The Colombian government agreed to the plan worked out by Venezuelan President Hugo Chavez, provided the aircraft carry Red Cross markings.
The rebels say they will free two women and a child but only to Mr Chavez.
They are among some 45 high-profile captives the guerrillas want to swap for some 500 rebels in Colombian jails.
The left-wing Revolutionary Armed Forces of Colombia (Farc) have been fighting the Colombian government for more than four decades.
The rebels hold several hundred hostages, some for political leverage but many also for ransom.
Mr Chavez was involved for several months in efforts to negotiate a prisoner exchange until Colombian President Alvaro Uribe ended his role in November, saying he had overstepped his mandate.
The deal would be the biggest hostage release in recent years
But last week the Farc rebels announced they would release three hostages to Mr Chavez or "whomever he opts to designate".
On Wednesday, Mr Chavez outlined his plans at a news conference in Caracas for what he called a "humanitarian operation".
"The only thing we need is authorisation from the Colombian government. We hope they will co-operate with us," Mr Chavez said.
Colombian Foreign Minister Fernando Araujo in Bogota then announced the approval of Mr Chavez's plan.
The rebels have offered to free Clara Rojas, an aide to former presidential candidate Ingrid Betancourt, kidnapped in 2002, and Ms Rojas's young son Emmanuel - who was reportedly fathered by one of her guerrilla captors.
The other hostage is former congresswoman Consuelo Gonzalez, who was kidnapped in 2001.
Under the plan, Venezuelan airplanes and helicopters, with representatives of France, Argentina, Brazil, Cuba, Bolivia and Ecuador and the International Committee of the Red Cross also on board, will fly to the Colombian city of Villavicencio.
From there, helicopters will fly to a site communicated by Farc rebels to the Venezuelan authorities.
A spokesman for the ICRC, Yves Heller, told Reuters news agency that it could take longer than a day to arrange.
"There are quite a few logistical and security details to be figured out. We are doing everything we can to ensure that the handover takes place as soon as possible," he said.
The BBC's Jeremy McDermott in Colombia says the rebels have got what they wanted by embarrassing their sworn enemy, Alvaro Uribe, a US ally.
In early December, Mr Uribe offered to designate a limited safe area to enable talks to take place aimed at exchanging rebel-held hostages for jailed rebels.
But the Farc want a larger zone in south-western Colombia to be demilitarised, a demand Mr Uribe has rejected.
The hostages' relatives are anxiously waiting for news
The freeing of the two women and a child would be the highest-profile hostage release during the presidency of Mr Uribe, who took office in 2002.
Ms Rojas, a 44-year-old lawyer, was kidnapped nearly six years ago along with Ms Betancourt, a French-Colombian national, during the latter's presidential campaign.
Mr Chavez has said he hopes another group of hostages might be freed later, including Ms Betancourt, whose release French President Nicolas Sarkozy has been seeking.