It looked as though Newcastle – who won 4-1 when the sides met at St James' Park last month – were going to leave Paris with all three points in the Group F encounter thanks to Alexander Isak's 25th-minute opener.
PSG had run out of ideas by the time they were gifted an opportunity to salvage a draw in injury time when the VAR decided a Tino Livramento handball in the box was worthy of a penalty.
Mbappé made no mistake, and PSG hold onto second place in the group behind Borussia Dortmund, who won 3-1 away to AC Milan and are through to the last 16.
The French champions will join them with a win in Dortmund in their final group game, while Newcastle now have to win at home to Milan and hope PSG slip up. "I feel it is a poor decision," Newcastle manager Eddie Howe said of the penalty. "It is hugely frustrating for us because at that moment you know how little time there is left in the game, but there is nothing we can do about it now." Howe's side would have been out with a defeat, so at least they remain in contention, while avoiding a third defeat in five group games allows PSG to hold off the threat of a first elimination from the Champions League before the last 16 in the Qatar era. "We should have won, without a doubt.