Marca reports that negotiations were held with the Argentine yesterday, when Mané was still in charge, but that everything had to wait until today to be finalised.
For Pochettino this will be his first job as a coach, but he is well loved amongst the fans at Espanyol from his playing days.
The 36-year-old had two spells with the Catalan side and racked up nearly 300 appearances, making him very much a fan favourite.
He is also reported to have good relationships with some of the players at the club, but unfortunately for him he will not have long to prepare for his first test.
Espanyol take on arch-rivals Barcelona in the Copa Del Rey tomorrow evening, and Pochettino will have just a day after a press conference this afternoon to work with the players.
Pochettino has become the third coach of the season for Espanyol, following the dismissal of first, Bartolomé Márquez, and then Mané late last night.
Whilst he comes in, there is likely to be another profile loss too, with sporting director Paco Herrera on his way out reportedly.
Herrera, who has been with the club for three years, could be facing the sack, and his dismissal could be announced this afternoon.
Espanyol are currently 18th in the La Liga table and worryingly for the new coach they are five points from safety.
James Walker-Roberts, Goal.com