The deal for de Paul was finalised by Valencia's South American representative, Roberto Fabian Ayala, with the deal also giving Racing a 10% cut of any future transfer.
The left sided midfielder was also a target for Italian Serie A side Udinese and also fellow La Liga rivals Granada and will join countrymen Pablo Piatti and also Federico Cartabia at the club.
The 19 year-old has made 55 appearances over three seasons for Racing which has also included a total of 6 goals as well.