The former Barcelona forward is set to reject a more lucrative offer from Saudi Arabian side Al-Hilal.
The Miami deal includes collaboration from brands like Adidas and Apple.
Messi, 35, won the Ballon d'Or award for the world's best player seven times and is expected to win it later this year after his World Cup success.
This is the first time Barcelona icon Messi has played outside Europe.
He wanted to remain in Europe for another season but, after no satisfactory offers were received, he had the straight choice between Inter Miami or Al-Hilal.
He was heavily tipped to be favouring a move to Saudi Arabia, where he would have joined Cristiano Ronaldo and Karim Benzema in the league in a deal that could not be matched financially.
But Messi was ultimately tempted to Major League Soccer (MLS) side Inter Miami for a variety of reasons including lifestyle, and a deal with big brands that extends beyond football.
He already owns a house in Miami, which he rents out.
He was keen on a return to Barcelona this summer but the Financial Fair Play limitations that will be in place for next season in La Liga made any ambitious plan to bring him back an impossibility.
Paris St-Germain won Ligue 1 in both his seasons at the club but went out in the Champions League last 16, which means his time in France was not seen as a huge success.
He netted 32 goals in 75 games for the club - and ended this season with 16 goals and 16 assists in Ligue 1.
Messi's two-year contract comes to an end this summer and both parties agreed to go their separate ways, with the forward suspended for two weeks in May for an unauthorised trip to Saudi Arabia.
His legacy comes from his time at Barcelona and winning the World Cup with Argentina in December.
He left Barca in 2021, after 21 years with the club, because of the club's financial problems.
Messi is Barcelona's record scorer with 672 goals and won 10 La Liga titles, four Champions Leagues and seven Spanish Cups.