David Beckham's plans to lead an MLS franchise in Miami have been boosted by long-awaited firm plans for a stadium to home the team.

A group led by the former England captain has reached an agreement with the city to build a 25,000-seater arena next to Marlins Park, home of the city's baseball team, Miami Mayor Tomas Regalado announced on Friday.

That deal should secure an MLS expansion team for the city, which will likely take to the league in 2018.

"This is a milestone," Regalado said at a news conference.

MLS currently fields 20 teams and is set to add a second Los Angeles franchise and teams in Atlanta and Minneapolis in the next three years. 

The league awarded a franchise to Miami in February 2014 with hopes it would begin play in 2016 - assuming a stadium site could be secured. That has proven more difficult than Beckham had hoped, as multiple proposed locations have been rejected.