The France forward, 24, had not been training with the first-team squad and was left out of PSG’s 0-0 season opener with Lorient on Saturday.
He has been in a contract stand-off amid a desire to join Real Madrid but could now extend his contract at PSG.
PSG said Mbappe was reinstated after “very constructive and positive” talks.
The France captain watched the game on Saturday from the stands.
Mbappe has one year left on his current deal and has so far refused to sign a new contract.
PSG chairman Nasser Al-Khelaifi has been adamant he would not let the striker leave for nothing and it is thought some kind of agreement is likely that will see Mbappe sign the one-year extension to his present deal as originally envisaged.
That would run to 2025 and allow PSG to sell Mbappe to Real next summer.
“Following very constructive and positive discussions between Paris St-Germain and Kylian Mbappe before the PSG - Lorient game, the player has been reinstated into the first team training squad this morning,” PSG said on Sunday.