Ntilikina spent four years with the New York Knicks, who drafted him eighth overall four years ago. Smith went ninth to the Mavericks, who traded the point guard to the Knicks a year and a half later in the blockbuster deal that brought Kristaps Porzingis to Dallas.
Ntilikina, 23, averaged 5.5 points and 2.7 assists with the Knicks. Born in Belgium, he moved to France when he was 3 and began his professional career in 2015 in a French pro league.
Ntilikina played in the Tokyo Olympics for France, which lost to the U.S. in the gold-medal game.
The Mavericks have focused on guards in free agency, adding veterans Sterling Brown and Reggie Bullock as they continue to build around star point guard Luka Doncic. Dallas also re-signed shooting guard Tim Hardaway Jr.