Garnett, a 19-year veteran in his first season with the Brooklyn Nets, has 25,352 career points.
Nowitzki, who has spent all 16 of his NBA seasons with the Mavs, has 25,361 after scoring 18 on Monday night.
For Nowitzki, he at least temporarily passed a power forward he has measured himself against his entire career. He legitimized himself as a superstar in the eyes of the Mavs' front office when Dallas swept Garnett's Minnesota Timberwolves in the first round of the 2002 playoffs, a series in which both power forwards put up monster numbers.
"He was the full package as a big guy," Nowitzki said. "All power forwards that came in had to look up to him.
"This is another great honor for me, but you know we're going to keep going back and forth. Obviously, we're both still active, but it's nice to be up there with a guy that's been around so long and has been effective for so long."
Nowitzki and Garnett could trade places on the all-time scoring list again Tuesday night, when the Nets have a road game against the Toronto Raptors. The Mavs' next game is at home Wednesday night against the Golden State Warriors.
However, it's likely that Nowitzki will create some distance between himself and Garnett on the all-time scoring list throughout the course of the season. Nowitzki is averaging 20.7 points per game this season. Garnett is averaging a career-low 6.5 points per game with the Nets.
Kobe Bryant, who ranks fourth all time with 31,617 points, is the only active player higher on the scoring list than Nowitzki and Garnett.