ESPN's Adrian Wojnarowski and Zach Lowe first reported the deal.
Mirotic has been one of the few bright spots for the struggling Pelicans this season, averaging 16.7 points and 8.3 rebounds in 32 games.
New Orleans acquired Mirotic from the Chicago Bulls last season, and he provided a significant boost for a Pels team that reached the second round of the playoffs.
The 27-year-old native of Montenegro averaged 15.6 points and 7.4 rebounds per game with the Bulls and Pelicans last season, both of which were career highs.
New Orleans exercised the club option in Mirotic's contract for 2018-19 after acquiring him, and things looked good for the Pelicans entering the season.
With Julius Randle joining a core of Anthony Davis, Jrue Holiday and Mirotic, the Pels were seemingly poised to equal or better their second-round playoff elimination at the hands of the Golden State Warriors last season.
Instead, injuries ran rampant throughout the team (including Mirotic, who has missed 22 games this season), and Davis requested a trade.
With the Pelicans potentially trading Davis at some point in the near-future, it made little sense to keep Mirotic in the fold, especially if there are no plans to re-sign him.
New Orleans has fallen out of the playoff race in the competitive Western Conference, and there was plenty of incentive to move on from Mirotic and get some assets in return for him since he was likely highly coveted given his versatility.
Mirotic is a stretch 4 who can shoot the three-ball effectively and rebound, which are two of the biggest factors in the current NBA landscape.
Things didn't work out for him in New Orleans from a long-term perspective, but he has developed into a valuable player who figures to play a significant role for the Bucks down the stretch.
Milwaukee has taken huge strides under head coach Mike Budenholzer. The team has the best record in the Eastern Conference (39-13) and the possible 2018-19 NBA MVP in Giannis Antetokounmpo.
Adding a versatile scorer to the roster gives Budenholzer more depth to play with as the Bucks chase the franchise's first championship since 1970-71.