Messi scored twice and converted in a penalty shootout too, carrying his side to victory over France after the greatest final in the competition's history ended in a 3-3 draw after extra time in Qatar on Sunday.
Kylian Mbappe scored a hat-trick for France - the first treble in a men's final for 56 years - as the world's top two players both shone in a wondrous duel in the Lusail Stadium near Doha.
Both men scored in the spot-kick shootout too but Argentina prevailed 4-2 to lift the World Cup for the third time, with Gonzalo Montiel scoring the clinching penalty to spark wonderful scenes of celebration in the stadium.
Argentina keeper Emiliano Martinez proved their hero again, saving Kingsley Coman's penalty and Aurelien Tchouameni then fired wide to give Argentina their first world title since 1986.
"This is my dream," said Martinez, who also won the Golden Glove as the tournament's best goalkeeper.
France had come from two goals down to level over 90 minutes with Mbappe netting twice in two minutes, first with an 80th-minute penalty and then a dazzling volley.
The France striker completed his hat-trick in the 118th minute with another spot-kick after Messi had bundled in what had looked likely to be the winner in the 109th minute.
Earlier, Argentina had dominated, going 2-0 up in the first half with Messi, who was making a record-breaking 26th World Cup appearance, converting a 23rd-minute penalty.
They then struck again with a sublime four-pass counter-attack involving Messi as Alexis Mac Allister's cutback found Angel Di Maria, who finished well.
In a final of extraordinary twists and turns, Mbappe became only the second man to score a hat-trick in a World Cup final following Geoff Hurst's treble for England in the 1966 victory over West Germany.
But it was Messi's day as the Argentine captain, considered by many to be the greatest footballer of all-time, was at last able to lift the one trophy that had eluded him.
Now there's no debate. Messi is definitively in the pantheon of soccer's greatest ever players, alongside Pele — a record three-time World Cup champion from Brazil — and Diego Maradona, the late Argentina great with whom Messi has so often been compared.
Here, Messi achieved what Maradona did in 1986, dominating a World Cup for Argentina - even though, at 35, he was 10 years older than 'El Diego' was when shooting them to the title in Mexico.
The torch will one day pass to Mbappe, whose late goals transformed the match and earned him the Golden Boot as the tournament's top scorer - but not yet.
"Let's go, Argentina!" Messi roared into a microphone on the field in the post-match celebrations, before he collected his Golden Ball award as the player of the tournament.
In 2014, Messi had also won the Golden Ball but the award gave him no pleasure as he received it in the Maracana after Argentina's 1-0 loss to Germany. This was different; he could not keep the smile off his face.
Then, as he waited to pick up the World Cup itself, he rubbed his hands in glee before collecting the trophy before joining his adoring teammates, for whom he has become even more of icon over the past month.
For as he lifted the biggest trophy in sport to the heavens, this was always going to be remembered as Messi's World Cup.
