The trade was made official Tuesday night.
"It is extremely important for our organization that we maintain our flexibility, and this trade helps us achieve that critical goal," Hawks general manager Travis Schlenk said in a statement released by the team. "We appreciate the contributions that Dwight made on the court and in the greater Atlanta community this past season."
Hornets GM Rich Cho said the team is excited to add "a player of Dwight's stature."
"He has been a very talented player, an elite rebounder and rim protector as well as a physical presence since the moment he entered the league," Cho said in a statement.
Howard signed a three-year, $70.5 million deal with his hometown Hawks in July but had a disappointing homecoming.
His averages with the Hawks -- 13.5 points and 12.7 rebounds per game -- were close to his production in the last of his three seasons with the Houston Rockets in 2015-16. Still, he finished the season unhappy about his diminished role in the playoffs, when he averaged eight points and 10.7 rebounds. He sat out the fourth quarter in two of six playoff games during the Hawks' first-round loss to the Washington Wizards.
"It was very difficult. I want to play," Howard said after the season. "I want to be on the floor. I want to make an impact. You can't do it on the bench."
On Wednesday, Howard tweeted a thank-you to the Hawks and their fans.
The Hawks were eliminated in the first round for the first time since 2014. Following the season, coach Mike Budenholzer resigned his additional role as president of basketball operations and Wes Wilcox stepped down as general manager. The Howard trade is the first deal for Schlenk, who faces the difficult challenge of re-signing free-agent forward Paul Millsap.
The trade will save the Hawks salary-cap space, and it signals that the franchise will look to rebuild and could move on from Millsap as well.
Sources told ESPN's Brian Windhorst that the Hawks have received inquiries about a possible sign-and-trade for Millsap, who could receive a max contract in that scenario.
Howard, 31, is due to earn $23.5 million for each of the next two seasons.
Plumlee, 28, still has three years remaining on his contract at $12.5 million per season. Belinelli, 31, is set to earn $6.6 million in the final year of his deal.
Howard has a history with Hornets coach Steve Clifford.
"Howard's best seasons came alongside coach Steve Clifford, and we believe their familiarity will make an immediate impact for the Hornets this upcoming season," Cho said.
Clifford offered his take on Charlotte's acquisition.
"I'm excited about working with Dwight again," Clifford said. "He brings a defensive mindset, shot-blocking ability and a level of physicality that will be a huge asset for us. We look forward to him continuing his career here in Charlotte."
Michael Jordan's Hornets have been attempting to land a star player for quite some time, and Howard potentially gives them that, provided he can return to playing at a high level.
Charlotte point guard Kemba Walker has developed into an All-Star, but Nicolas Batum struggled last season after being handed a $120 million, five-year contract -- the largest ever given to a Hornets player.
The trade also satisfies the Hornets' search for a true center since losing Al Jefferson to free agency last summer. They had hoped that Roy Hibbert would fill the role of a rim protector, but injuries slowed him down, and he eventually was traded to the Milwaukee Bucks in a midseason deal that brought Plumlee to Charlotte.
Plumlee wasn't much of a contributor last season for Charlotte, and he was beset by injuries.
The Hornets traded away their first-round draft pick in 2016 to acquire Belinelli after losing Courtney Lee and Jeremy Lin in free agency. Belinelli played in 74 games last season and averaged 10.5 points per game on 42.9 percent shooting.
Howard, an eight-time All-Star and three-time NBA Defensive Player of the Year, will be playing for his third team in three seasons.
Information from The Associated Press was used in this report.