Reed was arrested and charged with misdemeanor battery after an argument with his wife, Jasmine Reed, at their Miami residence on Aug. 5. Reed later entered into a pretrial diversion program.
In a statement Tuesday, the league said it conducted its own investigation and also consulted with domestic violence experts for guidance.
"The six-game suspension is based on all facts and circumstances of this matter and considers the conduct and its result, the outcome of the criminal matter, and Reed's voluntary participation in counseling as well as the court-mandated program, among other factors," the league said.
The National Basketball Players Association says it has filed a grievance with the league, saying it believes the six-game ban "is excessive and inappropriate."
The suspension will cost the center $65,000 of his one-year minimum $1.6 million salary.
The Pistons acquired Reed on Jan. 29 as part of the Blake Griffin trade.