MLS currently consists of 19 teams, with two more set to join in 2015
Miami has not had a Major League Soccer side since 2001, with the previous one having folded
Beckham confirmed plans to build a world-class stadium for the team
He said he would bring "the best" footballers to play for the club
No date has been sent for the completion of the stadium, or when the team would enter the league
He said a world-class stadium would be built to host the franchise, which would be the 22nd in MLS.
"I want to make this my own team," said the ex-Manchester United midfielder.
No date has been set for when the side would enter MLS.
Beckham's option to purchase a franchise
is believed to have been part
of the financial package he negotiated when he joined LA Galaxy in 2007. He played for the MLS club until 2012.
The former midfielder, who also had spells with Real Madrid, AC Milan and Paris St-Germain, added: "This is an exciting time for myself, my family, my friends and partners, and it is something we are really looking forward to bringing to Miami.
"We're planning to bring a team that will be a global team. I want to create a team that we can start from scratch and I am going to work hard for this city to make this team very successful. It is an exciting time.
"I have worked with some of the biggest clubs and greatest players and this is a dream."
Nick BryantBBC News in Miami
"Dotted with palm trees and heavily populated with Spanish-speaking residents, Miami is a north American city with a south American feel.
"So despite all the other sports the city has to offer - American football, baseball, basketball - it's a natural home for professional football, or soccer as it's called here. It also casts itself as one of America's glamour cities, which again suits the Beckham brand.
"When he signed as a player for Los Angeles Galaxy in 2007, a clause in his contract gave him the option of buying a team for the bargain price of $25m (£15.3m).
"Miami's last Major Soccer League team folded more than a decade ago, having reportedly lost some $250m (£153.1m). But that was partly because the team played in nearby Fort Lauderdale, and never had a purpose-built stadium.
"The new franchise plans to construct one at a waterfront location, where Caribbean cruise ships dock. It's a new departure for one of the game's biggest stars, not as a player but as an owner."
Beckham, who won the Champions League, the Premier League, La Liga and Ligue 1 as a player, would not confirm any names of players he wants to attract to Miami.
"We will bring great players in," he said. "The fortunate thing about my career is players are already interested in coming to Miami.
"The one thing I want to achieve is to set up a kids' academy. We want local talent, not just great players from abroad.
"The way the US team have improved has been incredible and the only way that will continue is to have good academies."
Beckham has long had an ambition to own a team in the US.
held talks with MLS
about the possibility of him buying a franchise shortly before his retirement, while basketball superstar LeBron James
said in November
that he was in discussion with Beckham about investing in the planned Miami club.
James reiterated his desire to be involved on Wednesday, telling reporters: "Right now, there are some things that need to be worked out but I think it's exciting for the city of Miami."
MLS currently consists of 19 teams, but the league announced in 2013 that
two further sides
would join in 2015.
Those will be Orlando City SC and New York City, which is part-owned by Manchester City.
The last MLS team in Miami folded after being in existence for four seasons. It struggled with sparse attendance and had the lowest revenue in the league.
Major League Soccer is hoping to add a new team in Miami, fuelled by the star-power of David Beckham and LeBron James.
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