After a goalless first half on Saturday in which the defense champions dominated but failed to convert, defender Theo Hernandez linked up with the electric Mbappé, whose shot ricocheted off Andreas Christensen’s heel and into the back of the net to give France the lead in the 61st minute.
Denmark leveled seven minutes later when Christensen made up for the deflection by firing a powerful header past distraught French goalkeeper Hugo Lloris.
Mbappé finished the job in the 86th minute, converting an Antoine Griezmann cross and pushing the ball into the back of the net with his thigh.
France leads Group D with six points, three ahead of Australia, who beat Tunisia 1-0 earlier in the day. The Danes and the Tunisians each have one point.
France will take on Tunisia and Denmark will meet the Socceroos in the final group matches.