Messi, 38, had not previously confirmed he would play in what will be a record-breaking sixth tournament for the Argentine superstar.
But it had been widely assumed the eight-time Ballon d’Or winner would again lead Argentina’s defence, four years after lifting the trophy in Qatar.
As well as confirming Messi’s presence, Thursday’s announcement notably excluded Real Madrid’s Franco Mastantuono from the Argentina squad.
Eighteen-year-old Mastantuono is considered one of the brightest prospects in Argentine football.
The largest ever World Cup, co-hosted by the United States, Canada and Mexico, kicks off June 11.
Argentina’s first match will be five days later against Algeria in Kansas City.
Messi has been at the heart of an injury scare in recent days, with his club side Inter Miami this week saying medical tests diagnosed him with muscle fatigue in his left hamstring.
The Major League Soccer club had provided no clear timetable for Messi’s return after his abrupt exit from Miami’s 6-4 victory over Philadelphia in the 73rd minute on Sunday.
But Scaloni had played down the seriousness of the injury this week.
The South American giants will journey to the United States for pre-World Cup friendlies against Honduras on June 6 and Iceland on June 9.
Their World Cup group also contains Austria and Jordan. (AFP)
