They won five championships and he was awarded as the MVP in seasons 2001-02 and 2002-03. Duncan, 40, provided no statement.
The 40-year-old Duncan, who was selected as the first overall pick in the 1997 National Basketball Association draft, spent his entire career with the Spurs - an anomaly in a league where players often change teams. He led the Spurs to a championship in his second season, in 1999, and was named Finals MVP.
Prior to the NBA, Duncan enjoyed a successful career at Wake Forest University in North Carolina. He and his wife Amy divorced in 2013.
Tim Duncan is calling it quits after nearly two decades as the face and backbone of the San Antonio Spurs. He is fifth on the NBA's career list in blocks, sixth in rebounds and 14th in scoring. Since drafting Duncan, the Spurs won five championships and posted a 1,072-438 regular season record, giving the team a.710 winning percentage, which is the best 19-year stretch in NBA history and was the best in all of the NBA, NFL, NHL and Major League Baseball over the last 19 years.
Ginobili wrote on Twitter: "Even tho I knew it was coming, I'm still moved by the news".
The announcement comes two months after the Spurs were upset by the Oklahoma City Thunder in the Western Conference semifinals, a six-game exit that immediately had people wondering yet again if it was Duncan's last hurrah.
The unassuming Duncan was the only player to start and win a title in three different decades.
Tim Duncan, the long-time star of the San Antonio Spurs, announced today that he is retiring.
Duncan was never one for big endorsement deals or look-at-me press conferences, which is why he was often overshadowed in the public eye by more outsized personalities like James and Kobe Bryant, who also retired this year after 20 seasons, all with the Los Angeles Lakers.
Duncan totaled 15 All-NBA Team selections (tied for most all-time) and 15 NBA All-Defensive Team honors (most all-time), garnering both honors in the same season 15 times, the most in league history.
Duncan and Spurs coach Gregg Popovich also formed a dynamic duo, accounting for the most wins ever by a player-coach duo at 1,001.
He would go on to win four more titles, in 2003, 2005, 2007 and 2014, and was named Finals MVP twice more, in 2003 and 2005.