The acquisition comes hours after the Braves added fellow outfielder Adam Duvall in a trade with the Miami Marlins for catcher Alex Jackson. Duvall hit .229 and ranks among the top 10 in the National League with 22 home runs and 68 RBIs in 90 games for Miami this season.
Soler, 29, is batting .201 with seven home runs and 18 RBIs. He has failed in the past two seasons to match his breakout 2019 season, when he played all 162 games and hit a Royals club-record 48 homers, but will still provide a strong right-handed power bat to the Braves' lineup.
Kalich, a 2019 fourth-round draft pick who will be assigned to Class A Quad Cities, had a 3.26 ERA with five saves in five opportunities for High-A Rome this season.
The Braves needed to revamp their outfield as they attempt to remain in the hunt for a fourth consecutive NL East title. Atlanta suffered a severe blow to its playoff hopes when it lost Ronald Acuna Jr. to a season-ending knee injury on July 10.
Braves left fielder Marcell Ozuna, who was on the injured list, is facing domestic violence charges following an arrest at his home in May. He has not played since.
Rookie Cristian Pache, who opened the season as the Braves' starting center fielder, hit only .111 in 22 games. Atlanta released three-time Gold Glove winner Ender Inciarte on Thursday.
"There's no doubt we've had our challenges. The one thing that's fortunate for us is we're playing in the NL East in 2021," general manager Alex Anthopoulos said, highlighting how fortunate the Braves are to be in the NL East, where any team close to .500 is still relevant. "We're all in it.''
In a separate trade, Atlanta also acquired right-hander Richard Rodriguez from the Pittsburgh Pirates for two minor leaguers. Manager Brian Snitker said Will Smith, who has 21 saves in 23 opportunities, will keep the closer's role.
"He's probably one of the top guys in terms of save opportunities and saves,'' Snitker said.
The Braves traded two right-handers -- Bryse Wilson, who is 2-3 with a 4.83 ERA in Atlanta this season, and minor leaguer Ricky DeVito -- to Pittsburgh in the deal.
The Associated Press contributed to this report.