The former England midfielder appeared at a news conference in Miami to make the announcement.
Beckham said: "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."
Beckham, who retired from playing last year, said he planned to make the new team a globally-recognised club.
He said: "We are going to make a soccer club that is going to be loved my millions of people - we plan on bringing a team that is not just for Miami but is a global team."
Beckham's group is now in talks with Miami local government officials about building a stadium for the new club, but he insisted no public money would be needed.
He said: "We don't want public money, we will fund the stadium ourselves, it is something that we have worked very hard on.
"Nothing successful in life is easy, there are going to be bumps along the way and you have to go through certain tough times to come out at the end being successful.
"We are going to have the right investors, and I'm not just talking about wealth but people who have a passion for the game as well."
Beckham said he would not be making an approach to his former manager at Manchester United, Sir Alex Ferguson, to coach his team.
He added: "He is a great manager and gave me the chance to play for my boyhood dream club, but unfortunately he has retired so we won't pull him out of retirement, I think he is enjoying that."