The France superstar was on the losing side of an epic final against Argentina that was settled in a penalty shootout after a 3-3 draw on Sunday.
He looked so crestfallen afterwards that he had to be consoled on the field by French President Emmanuel Macron.
Mbappe had been the leader France desperately needed as time was running out with the defending champions trailing 2-0, and, in truth, he had been practically invisible up to that point.
But his two goals in less than two minutes carried France back into the match. Twice. Mbappe first converted a penalty in the 80th minute, and then he scored with a superb volley from just inside the area in the 81st.
It took only 97 seconds for him to get France even with Argentina and the great Lionel Messi.
Mbappe scored a second penalty late in extra time, in the 118th minute, about 10 minutes after Messi had given Argentina the lead again.
Mbappe's hat-trick was only the second in a World Cup final — the first was by England striker Geoff Hurst in 1966.
The Frenchman leaves Qatar with the Golden Boot trophy as the tournament's top scorer with eight goals. He's quickly closing in on Pele's 12 career World Cup goals - and he's still only 23.
But Mbappe couldn't quite match the Brazil great's back-to-back World Cup titles — both players were teenagers when they won their first one, Pele in 1958 and Mbappe in 2018.
Mbappe tried to set the tone in the penalty shootout, taking responsibility for the first kick. He converted the penalty but France ended up losing 4-2.
Messi did the same for Argentina to start the shootout, but his teammates all scored their penalties.
After the shootout, Mbappe made sure he was the first to console Kingsley Coman and Aurelien Tchouameni after their slow walks back from the spot following their failure to score.
Mbappe stood bent over in the centre circle, hands on his knees, as Argentina defender Gonzalo Montiel prepared to take the decisive kick. He then squatted, saw the net ripple and walked away alone amid the Argentina celebrations.
France coach Didier Deschamps came over to console him, but Mbappe went to the team dugout and sat slumped in a chair with his dark blue shirt pulled over his face to hide his emotions.
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