Sources told ESPN.com that Martin, who cleared waivers early Friday after negotiating a buyout earlier this week with the Minnesota Timberwolves, has chosen San Antonio after being pursued by a number of playoff-chasing teams, including the Houston Rockets and Dallas Mavericks.
But the chance to join a team with the Spurs' championship pedigree proved impossible to pass up, especially since San Antonio began its pursuit aggressively from the moment ESPN.com reported last week that Martin and the Timberwolves had entered into buyout talks.
Days of protected talks between the sides ultimately resulted in an agreement late Tuesday before the midnight deadline that kept Martin playoff-eligible this postseason.
The Spurs (52-9) will have to release a player to make roster room for Martin.
Martin, 33, has averaged 17.6 points in 30.5 minutes per game for his career and has long been regarded as a high-efficiency player with a propensity to get to the free throw line. He's also a lifetime 38.5 percent shooter from 3-point range.