He will reportedly receive $6 million over the length of the contract.
Belinelli, 27, averaged 9.6 points and two assists, but only shot 35.7 percent from beyond the arc in 79 games last season with the Chicago Bulls.
Belinelli was a good player off the bench in his first season with the Bulls, and has a career scoring average of nine points a contest. He was an expendable player after the Bulls drafted shooters Tony Snell and Erik Murphy last month.
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The Spurs' agreement with Belinelli comes after they struck deals with two of their own free agents: guard Manu Ginobili (two years, $14 million) and center Tiago Splitter (four years, $36 million).