The 31-year-old Brown has played in 39 games for New Orleans this season, starting all but two games. He is averaging 9.7 points per game and has made nearly 37 percent of his shots from 3-point range.
"Devin is a tough kid who can spread the defense with his shooting ability," Bulls coach Vinny Del Negro said. "Aaron was a great guy who worked hard. He just really didn't get much of an opportunity, especially after he got injured early in the year. I think it made sense for both teams."
The Bulls this year have missed the scoring of guard Ben Gordon, who signed with Detroit before the season. The trade was announced Monday, before Chicago played at San Antonio and the Hornets at Portland.
Del Negro said Brown gives the Bulls more backcourt depth and could also be an option at small forward. Brown is expected to join the team Tuesday in Oklahoma City.
The move opens the way for rookie Marcus Thornton, who has averaged 9.4 points in only 18.6 minutes per game, to start for the Hornets. It also brings New Orleans within about $424,000 of getting under the NBA's luxury tax threshold.
Gray, who is 25 and in his third NBA season, averaged 2.3 points and two rebounds in eight games this season with the Bulls.