The meeting, which will take place in international waters near the coasts of Zaire, Angola and Gabon, was announced in Kinshasa yesterday evening by the US ambassador to the United Nations, Bill Richardson.
An upbeat Mr Richardson said the talks would be "an historic occasion that hopefully will lead to a peaceful transition in Zaire".
The announcement came despite earlier signals from Mr Mobutu's camp that the President, who is 66, had no intention of meeting Mr Kabila on the ship.
There is speculation in Kinshasa Mr Mobutu's about-face could be a sign he is buckling under international pressure to stand down gracefully before the rebels attack the capital.
With the rebels within striking distance of Kinshasa and controlling all Zaire's mineral wealth, the "Great Leopard" has few cards left to play if and when he does sit down with Mr Kabila.
Mr Mobutu attended the announcement at his Kinshasa palace yesterday but looked weak and unwell and did not address the media. He is still officially convalescing from surgery for prostate cancer undergone in Switzerland last year.
The announcement of the breakthrough followed two days of shuttle diplomacy by Mr Richardson, who first met Mr Mobutu on Tuesday before flying on to the rebel-held town of Lubumbashi for consultations with Mr Kabila.
Mr Richardson presented Mr Mobutu with a letter from Bill Clinton which, according to US newspaper reports, repeated the President's earlier advice to Mr Mobutu to stand down in a dignified fashion.
Mr Kabila had said he would meet Mr Mobutu on the South African vessel even before Mr Richardson met him on Tuesday, but he added: "As far as I am concerned this will be a short ceremony at which Mr Mobutu is supposed to agree to leave, otherwise our forces now advancing on the route to Kinshasa will eject him."
Speaking to reporters yesterday, Mr Richardson said that there were no preconditions or agenda for the meeting, and nor was there any agreement for a ceasefire. He hoped this would come as a part of a step-by-step process, beginning with face-to-face talks and leading to a ceasefire and a political framework for a transition leading to elections.
"I want to commend the statesmanlike action of President Mobutu and Mr Kabila for this act of reconciliation," he said. "Mr Kabila agreed to these talks and venue last night in a meeting in Lubumbashi, and President Mobutu, in statesmanlike and patriotic fashion, agreed to the talks a few minutes ago."
The negotiations will take place under UN auspices and will be attended by a number of other African leaders, Mr Richardson said.
He praised South Africa's President Nelson Mandela and Gabon's President Omar Bongo for their role in encouraging and facilitating the process. "The United States is proud to have played this catalyst role, but now it's time for Zaireans and Africans and the United Nations to bring around this peaceful transition."Reuse content