The German joins Kobe Bryant as the only other player to spend more than two decades with the same team.
Dirk Nowitzki set to pass 20 years with Dallas Mavericks after signing new contract
Dirk Nowitzki will become only the second player to spend 20 NBA seasons with the same team after signing a new deal with the Dallas Mavericks on Thursday.
A statement from the Texas franchise said Nowitzki will join retired Los Angeles Lakers legend Kobe Bryant as the only other member of the 20-season club when he returns for the 2017/18 campaign.
US media reports earlier on Thursday said Nowitzki had signed a two-year $10 million (Dh36.7m) contract which would see him play on for two more seasons.
ESPN reported that the Maverickss had agreed the deal after declining to take up a $25m team option on Nowitzki, widely regarded as the team's greatest ever player. Terms of the deal, including the length of Nowitzki's contract, were not revealed on Thursday.
There was little doubt that Nowitzki, 39, would remain in Dallas after indicating in April he wanted to stay on for at least one more season.
Nowitzki averaged 14.2 points in 54 games last season, his lowest average since his rookie season of 1998/99 when he contributed 8.2 per game.
Nowitzki has appeared in a franchise-record 13 NBA All-Star Games, and earned 12 consecutive All-NBA Team selections (2000-12). He was named Most Valuable Player of the 2006/07 season and voted MVP of the 2011 NBA Finals.
Nowitzki became only the sixth player in NBA history to reach the 30,000-point mark this year when he broke the barrier in March.
The power forward has scored 30,260 points, making the top foreign scorer in the NBA of all-time. The Mavericks finished outside the playoff places in 11th spot this season with a 33-49 record
* Agence France-Presse