Elliott's suspension comes in the wake of an investigation into domestic violence allegations, stemming from an incident a year ago in Columbus, Ohio. In September, the Columbus City attorney's office in OH announced that Elliott wouldn't be charged because of conflicting and inconsistent information.
The No. 4 overall pick of the 2016 draft, Elliott earned All-Pro honors as a rookie, rushing for 1,631 yards and 15 touchdowns.
Elliott has three days to appeal the decision.
The NFL has cracked down on domestic violence allegations in recent years, and a 2014 revision of its personal conduct policy gives Commissioner Roger Goodell the ability to suspend players with or without a conviction.
Elliot will be able to participate in preseason activities, but with the suspension taking effect he wouldn't be eligible to return to the team's active roster until October 23.
The former Ohio State Buckeye led the National Football League in rushing last season with 1,631 yards in addition to 15 touchdowns. With Elliott sidelined, Dallas will likely turn to Darren McFadden, Alfred Morris and Rod Smith at running back.
The NFL alleged Elliott used "physical force" in July 2016 during altercations with his ex-girlfriend resulting in her sustaining injuries.
In most gambling establishments, the Cowboys had been the odds-on favorite to come out of the NFC.
Cowboys owner Jerry Jones said last week that he did not expect a suspension to be coming for Elliott.
During an NFL conference call Friday, NFL officials said the league considered both Thompson's allegations and a separate March 2017 incident in which Elliott pulled down a woman's shirt at Dallas' St. Patrick's Day parade in their investigation.