The 36-year-old was presented in front of a sell-out 20,000 crowd at the DRV PNK Stadium on Sunday.
Fans were made to wait for the seven-time Ballon d'Or winner to appear after the unveiling was delayed due to bad weather conditions.
Messi, who will wear the No.10 shirt, took centre stage as he was joined by former Barcelona teammate Sergio Busquets.
As the World Cup winner was walking on the pitch and taking in the admiration of the crowd, ten-year-old Thiago could not resist nutmegging his famous father.
Messi then turned around as the youngster lifted his arms in the air.
READ MORE ON TRANSFERS
Rashford agrees new Man United contract in double boost for club with Onana deal agreed
Henderson's decision, Kane latest, and Onana deal soon as transfer window bursts into life
On joining the club, Messi said: "I really want to start training, to compete. I have the same desire that I always had to compete, to want to win, to help the club continue to grow.
"I am very happy to have chosen to come to play in this city with my family, to choose this project and I have no doubt that we are going to enjoy it a lot.
"We are going to have a good time and very good things are going to happen."
Inter Miami co-owner David Beckham told Messi: "We are so proud that you have chosen our club for this next stage in your career - and we're also delighted to welcome your beautiful family."
Most read in Football
Chelsea transfer news LIVE: Blues sign wonderkid, Caicedo bid readied, Lukaku latest
Man United agree Onana fee and Rashford contract, Messi unveiled in Miami, Lukaku in limbo
Man United transfer news LIVE: £47m Onana deal agreed, Rashford to sign new contract
Chelsea agree to sell forgotten man to Leeds with £7million fee agreed
Many view Messi as the GOAT (greatest of all time), with one fan taking this viewpoint to an extreme by bringing a real life goat with fans posing alongside the animal outside the stadium.
The football icon will look to inspire his side up the MLS table with the Florida-based rock bottom of the Eastern Conference, managing just 18 points from 22 games.
Inter Miami are without a victory since a 2-1 win over New England on May 14.
Their winless run stretched to 11 matches with their latest outing seeing them lose 3-0 against St. Louis City on Saturday.