The Pelicans will receive second-round picks from the Bucks in 2019 (via Denver), 2020 (two, via Washington and Milwaukee) and 2021 (via Washington).
Mirotic, who is making $12.5 million this season, will be an unrestricted free agent this summer. In 32 games this season, he is averaging career highs in points (16.7) and rebounds (8.3). He's also making 2.7 3-pointers per game, tied for ninth in the NBA.
The Bucks are averaging 13.3 made 3-pointers per game, which ranks second behind Houston (15.4).
Johnson, 22, is averaging 7.5 points and 3.6 rebounds in his fourth NBA season. He was the eighth overall pick in the 2015 draft.
A first-round pick in 2007, the 32-year-old Smith is averaging 3.2 points and 2.7 rebounds this season. He joined the Bucks after being acquired from Washington in a three-team trade in December that also included Cleveland.
ESPN's Tim Bontemps contributed to this report.