ESPN's Josina Anderson was the first to report the story.
"It’s a trade that we feel it was an opportunity that I couldn't pass on to get a first-round pick. In this business here, I thought that was invaluable for me. It was something I felt like I had to do," Raiders general manager Reggie McKenzie told reporters, according to Michael Gehlken of the Las Vegas Review-Journal.
Dallas has been in desperate need of a top-end wide receiver and is likely banking on Cooper to rediscover his Pro Bowl form. Cooper was named to the Pro Bowl in 2015 and '16, but posted the worst totals of his career last season.
This year, Cooper's recorded 22 receptions for 280 yards and a touchdown through six games.
"I hate to see good players go ... I was on the practice field when Reggie came to me and said (the) Cowboys would do this for a No. 1, and I said let's do it," Raiders head coach Jon Gruden said, according to ESPN's Chris Mortensen. "We now have five No. 1 picks in the next two years, so I'm excited about that."
McKenzie added that Cowboys executive vice president and CEO Stephen Jones called earlier Monday to finalize the trade.
"He wanted the player, and he gave me the pick. That’s what it came down to," McKenzie said.
Cooper was selected fourth overall by the Raiders in the 2015 draft out of Alabama. He's currently owed $13.92 million in base salary for the 2019 season before becoming an unrestricted free agent.
McKenzie wished Cooper well and believes he has a bright future with the Cowboys.
"I think he’s a first-round player. ... Has he been inconsistent? Absolutely. But has he shown greatness? Absolutely. ... This guy is still a young player. I think he’s going to do well down there in Dallas," McKenzie said.
Oakland now holds three first-round picks in the 2019 draft: their own, Chicago's (acquired in the Khalil Mack trade), and now Dallas'. The Raiders also received Chicago's 2020 first-rounder in the Mack deal.