Per Shams Charania of The Athletic and Stadium, Porzingis agreed to a five-year deal worth $158 million to stay with the Mavs.
Charania reported Tuesday that Dallas planned to offer Porzingis a full five-year extension as soon as free agency started.
The Mavs acquired the 23-year-old in January from the New York Knicks. He didn't appear in a game last season while recovering from a torn ACL, but he figured to be a big part of the plan for 2019-20 in Dallas.
Charania reported in January the former All-Star was intent on signing his qualifying offer with the Mavericks.
Dallas head coach Rick Carlisle provided reporters with an update on Porzingis' rehab plan in March:
"It's pretty obvious that (sitting out the remainder of this season is) an opportunity to gain strength, to make sure that he is back 100 percent. Beyond that (Porzingis' camp) had a plan in place, and we're helping to facilitate them executing their plan.
"I know that our trainers, strength coaches and medical are adding value to it, so it's a win-win as far as I can see."
Despite being 23, Porzingis has a lot to prove in 2019-20. He's missed 142 out of a possible 328 games in four NBA seasons because of injuries. He admitted to taking a more conservative approach to rehabbing his ACL because "there is no protocol for a 7'3" guy."
When he has been able to play, he's shown tremendous promise. The Latvian star was having a career-year with 22.7 points and a 39.5 three-point percentage for the Knicks in 2017-18 before blowing out his knee.
Assuming his rehab has gone smoothly, he should have a significant impact on the court next season.
The Mavs have high hopes for 2019-20 with Porzingis and Luka Doncic leading the franchise. It may take time for him to get back in peak playing shape, but his ceiling is so high that this deal is a risk worth taking for Dallas.