Messi, 34, dropped to the ground in joy at the full-time whistle and was swiftly mobbed by his team-mates, before being hurled in the air in celebration, as he finally claimed top-level honours with his country in his 10th major tournament.
He also helped end Argentina’s 28-year spell since they last won the competition and was named player of the tournament after his four goals in the competition.
Angel di Maria proved the matchwinner with his superb lob, after taking down Rodrigo de Paul’s lofted pass.
Messi had a chance to sign off the win but slipped with the goal at his mercy, in what would have been the perfect finale for the Argentine captain.
Defending champions Brazil were disappointing, with their only chances of note coming when Richarlison and Gabriel Barbosa forced saves from Emi Martinez.
In a contrast of emotions, Messi’s opposite number 10 and former Barcelona team-mate Neymar sank to his knees in tears at the final whistle, as his own personal pursuit of international success continues, having missed Brazil’s 2019 Copa win through injury.
The pair, who played together at the Nou Camp between 2013 and 2017 before the Brazilian’s move to Paris St-Germain, embraced in a long-lasting hug while they waited for the trophy ceremony.