The 1999–2000 NBA season was the Mavericks' 20th season in the National Basketball Association. During the offseason, the Mavericks re-acquired Sean Rooks from the Los Angeles Lakers. This season is especially notable as Mark Cuban purchased the team from H. Ross Perot, Jr. in January 2000. Under Cuban's leadership, the Mavs built a foundation for continued NBA success that eventually led to two Finals appearances (and one championship) in the next decade.

The Mavs signed flamboyant power forward Dennis Rodman in early February, after Cuban bought the team. Rodman's behavior issues led to a very short (12 game) tenure in Dallas before he was waived. Michael Finley averaged 22.6 points per game and was named NBA All-Star for the first time in his career, as he was selected to play in the 2000 NBA All-Star Game in Oakland. Second-year star Dirk Nowitzki showed improvement averaging 17.5 points per game. The Mavericks posted a 9–1 record in April and finished fourth in the Midwest Division with a 40–42 record. However, they missed the playoffs for the tenth straight season.

Following the season, Cedric Ceballos was traded to the Detroit Pistons, Erick Strickland was traded to the New York Knicks, Rooks was traded to the Los Angeles Clippers, and Robert Pack was dealt to the Boston Celtics, who then sent him back to the Denver Nuggets.

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