MLS Commissioner Don Garber made the announcement alongside the club's ownership group, including Carolyn Kindle Betz, the Taylor family and Jim Kavanaugh.
With Betz and six other female members of the Taylor family part of the group, St. Louis becomes the first female majority-owned club in MLS history and one of few in professional sports.
The club will begin MLS play in 2022, in a new stadium.
The St. Louis Post-Dispatch had reported last week that the city known for its giant Gateway Arch would land an MLS team.
Twenty-four teams are playing in MLS this season, including first-year club FC Cincinnati.
David Beckham's Inter Miami squad and a new team in Nashville, Tennessee, are set to debut in 2020 with a club in Austin, Texas, scheduled to open in 2021.
Two NFL clubs have departed St. Louis, the Cardinals leaving for Arizona in 1987 after 28 seasons and the Rams, who arrived from Los Angeles in 1995, won the Super Bowl in 2000, but returned to Southern California in 2016.
The city is home to Major League Baseball's Cardinals and the Stanley Cup champion Blues in the National Hockey League.
The idea of an MLS club in St. Louis, however, seemed dim two years ago when voters denied the use of a business tax to finance a new stadium.
The revamped ownership group revived prospects for the club, with MLS saying in April that St. Louis was a contender for an expansion franchise at a price tag of $200 million.