Minto, who joined Chelsea from Charlton in 1994, is out of contract at Stamford Bridge and the club will receive no fee for the player.
The impending arrival of 18-year-old Nigerian international Celestine Babayaro from Anderlecht is believed to have unsettled Minto, who could not agree improved terms at Chelsea.
Toni Oliveria, the Benfica director of football, confirmed the player had signed until 2000 having passed a medical and would be arriving in Lisbon for the new season in August.
"We have finalised all the details with the player and his representatives which had been our objective in going to London," Oliveria said.
With Chelsea currently touring the Far East, no official confirmation of the move was available last night. Earlier this week, the club denied the move.
In Spain, the Ronaldo saga dragged on yesterday when the Brazilian striker criticised the Barcelona president, Jose Luis Nunez, and said that he will be leaving the club.
"Everything Nunez has said is a lie and we no longer need to negotiate with them," Ronaldo said. "He tells me one thing and my agents something else. He has been cheating us for seven month. It's sad, but I'm leaving."
This explanation came after 24 hours of negotiations, in which Ronaldo's agents appeared to accept, and then pull out of, a deal to improve his contract. One of the sticking points in the negotiations was whether a bonus payment of two billion pesetas (pounds 8.75m) should be paid in Spain or in a tax haven.
A club spokesman said yesterday that the talks had broken down but added that Ronaldo remained a Barcelona player. It is assumed that Internazionale will shortly pay the 4.5 billion pesetas (almost pounds 20m) necessary to free Ronaldo from his existing contract, although Lazio have upped the ante in their efforts. Sergio Cragnotti, the Lazio owner, has reportedly offered an annual salary of more than pounds 3m, comfortably more per year than Ronaldo has demanded.
Barcelona's spokesman said Ronaldo would not play again for the club this season. The Brazil striker will therefore sit out the Spanish Cup final against Real Betis on 28 June as well as three league games he had been expected to miss because of international duty. At present, he is in Norway for Brazil's game tomorrow.
The 20-year-old has scored 34 goals this season and is considered one of the main reasons Barcelona won the European Cup-Winners' Cup, stand second in the league, two points behind Real Madrid, and have reached the final of the Spanish Cup.
Nunez has taken the news of Ronaldo's departure philosophically. "We've saved ourselves 15 billion pesetas over 10 years," he said.Reuse content