PSG manager Thomas Tuchel named the French superstar to his side's bench for the quarterfinal clash in Lisbon now that Mbappe has recovered from an ankle injury he suffered in July.
With the 21-year-old unable to feature from the opening whistle, Tuchel opted for Pablo Sarabia, Neymar, and Mauro Icardi to lead the line; the Ligue 1 champions are also without the suspended Angel Di Maria.
Mbappe was in a race against the clock after a hefty tackle in the French Cup final against Saint-Etienne on July 24; Tuchel previously said it would take a "miracle" for the young forward to be fit in time for Wednesday's contest.
PSG are also missing midfielder Marco Verratti, who's dealing with a calf injury.
"We must wait and be patient with Marco," Tuchel said earlier this week.
"Last week he couldn't run. He has just started again but it is going to be very tight for the semifinals. But we will try everything like we have done with Kylian."
Atalanta, meanwhile, are without Josip Ilicic, who is home in Slovenia tending to a personal matter.