Da Matta has been bought out of his contract with the Newman-Haas Cart team, and the 29-year-old will move to F1, according to sources close to the deal.
Toyota, which supplies engines to Newman-Haas, were unavailable for comment.
Da Matta admitted for the first time last weekend that Toyota had offered him a drive, but insisted he had not yet made up his mind about what to do.
"The decision is very important for me. For you it may seem easy, but for me it's a pretty difficult decision. That is the only reason why it's taking so long," Da Matta said.
A Toyota spokesman said at the time that the team were "in close contact" with Da Matta, but were not yet in a position to make an announcement.
Da Matta will follow in the tracks of former Cart champions Juan Pablo Montoya and Jacques Villeneuve in moving to F1.
The move leaves Minardi and Jordan as the only teams with seats open in 2003.
Jordan have Takuma Sato under contract, but his position is under threat and he may be replaced by Eddie Irvine or Anthony Davidson.