The contract, which can't be signed officially until July 10 when the league lifts its annual moratorium on player business, is a two-year deal worth $5.6 million, sources said.
The deal with Belinelli likely signals the end of the Spurs' association with guard Gary Neal, who helped San Antonio win Game 3 of the NBA Finals with his breakout six 3-pointers and 24 points.
Sources told ESPN.com on Thursday that Neal has been receiving offers in restricted free agency at a higher price than San Antonio is willing to match, which is among the factors that prompted the Spurs to move quickly to come to terms with Belinelli.
It's seen as a near certainty in San Antonio that Neal will sign an offer sheet with another team later this month that the Spurs will have three days to match or pass.
Belinelli, meanwhile, received more lucrative offers elsewhere -- most notably from Cleveland -- after averaging 9.6 points a game on 39.5 percent shooting and 35.7 percent shooting from 3-point range last season with Chicago.
But Belinelli, sources said, couldn't resist joining the Spurs' roster with its many international players.