He announced the move via Twitter:
The Mavericks and Doncic's former team, Real Madrid, reached a buyout agreement Saturday, opening the way for Dallas to negotiate with the rookie.
The 19-year-old was originally drafted by the Atlanta Hawks and then shipped to Dallas in exchange for the draft rights to Trae Young and a protected 2019 first-round pick.
Considered perhaps the greatest Euro prospect in history, Doncic will join a promising backcourt with Dennis Smith Jr., the ninth overall pick from a year ago.
After the Mavs acquired the Slovenian, Dallas head coach Rick Carlisle told reporters:
"Luka Doncic was the guy we targeted to get in this draft if there was any way possible to do it. At one point, we thought there might be a slight chance he could fall to us, but a couple of days ago it was pretty clear that there was no way that was going to happen. He's just too good. We get a guy we think is franchise foundation piece."
Based on his resume, there was no better player in this class.
Doncic is the youngest Euroleague MVP and Final Four MVP in history by a long shot and spent most of his formative years playing against men 10-plus years his senior. He led Real Madrid to Euroleague and ACB championships on his way out, including a Spanish league title two days before the draft.
"Honestly, it's like a dream," Doncic told the media. "I've been dreaming about being a Euroleague champion, being a European team champion, being drafted. All this year has been like a dream."
In contrast to nearly every other player selected in June, Doncic will take a break before making a proper NBA debut.
The Mavs have been resting him in summer league. Doncic has essentially been competing for 18 months straight; he's perhaps the only player who will be playing less basketball in the NBA than he did prior.
The contract Doncic signed is scaled, so it would take historically poor play for the teenager to miss out on the third and fourth years of that deal, options teams almost universally accept for high draft picks—barring some type of Anthony Bennett situation.
Now Doncic can begin his NBA career, with the Mavs hoping they're replacing one all-time Euro great with another.