He is expected to be joined at the club by former Barcelona team-mate Spanish midfielder Sergio Busquets, while ex-Argentina and Barcelona coach Gerardo “Tata” Martino recently took over as coach.
Miami owner Jorge Mas has suggested Messi and Busquets could be part of “three to five” new signings for the South Florida club in the current transfer window.
Another former Barca player, Spanish full-back Jordi Alba, has also been strongly linked with a move to the team, which is co-owned by former England and Manchester United star David Beckham.
Messi is expected to make his debut for his new club in the July 21 Leagues Cup match against Mexican club Cruz Azul.
Miami are currently bottom of MLS’s Eastern Conference with just five wins from 21 games and are ranked 28th out of the 29 teams in the league.
But the club are in the semi-finals of the US Open Cup, where they have been drawn against league-leaders FC Cincinnati.
The seven-times Ballon d’Or winner has spent the last two seasons at Paris Saint-Germain, after moving from Barcelona in 2021, where he spent the majority of his career.
During his time with Barca, Messi won ten Spanish league titles, seven Copa del Rey (Spanish Cup) titles and four Champions League winners medals.
He scored twice for Argentina in the World Cup final which they won on penalties in Doha in December, after the game ended 3-3 after extra-time and raised the trophy as captain.