Denmark equalized seven minutes later thanks to Andreas Christensen’s terrific header past French goalkeeper Hugo Lloris.
Mbappé made it 2-1 in the 86th minute by driving the ball into the back of the net with a thigh after a cross from Antoine Griezmann.
France leads Group D with a perfect score after two victories. Australia, which beat Tunisia 1-0 earlier on Saturday, is second with three points. Denmark and Tunisia stayed at one point.
In the final day on Wednesday, France will face Tunisia and Denmark will clash with the “Socceroos”.