Ajax stand to make another €11m in add-ons if De Jong succeeds at Camp Nou, where he has penned a five-year deal, taking him up until the end of the 2023-24 campaign. De Jong will remain with Ajax until the end of the season before making the switch to Barca in the summer.
"De Jong is one of Europe's most promising midfield talents," Barcelona said in a statement. "At just 21 years of age, he is joining the club after proving himself as a multifunctional player with an excellent reading of the game and the ability to provide the killer pass."
For most clubs, losing top talent is a killer. For Ajax, it's their business model.
The Catalan club's pursuit of De Jong dates back to 2016. Former sporting director Robert Fernandez is a long-term admirer of the Netherlands international, and they made two bids for him last summer. However, Ajax sporting director Marc Overmars said they were nowhere near the Eredivisie's valuation of the player.
Having failed with those offers, Barca decided to park their interest until the end of the season. But the emergence of PSG forced them to act quickly.
A Barca delegation flew to Amsterdam last Thursday, sources confirmed to ESPN FC, in the belief that De Jong was leaning toward PSG's offer. While in the Dutch city, they upped their previous bid and promised regular playing time -- which was one of De Jong's major concerns, given the competition for midfield spots in Ernesto Valverde's side.
Even on Tuesday, Barca were still not sure if they had done enough. Sporting director Eric Abidal said that all the club could do was wait for De Jong's decision, knowing that they faced fierce competition for his signature.
One of those competitors was Manchester City, with ESPN FC sources saying Pep Guardiola's team were interested in De Jong but never got as far as making a bid for him because he seemed set on a move to Barcelona and his salary and bonuses were too much to match.
And indeed later on Tuesday, Barcelona received information that De Jong wanted to join them. Not wanting to risk another Antoine Griezmann situation -- they thought they'd signed the French forward last summer only for him to renew with Atletico Madrid -- plans were quickly made to get contracts drawn up and signed as quickly as possible.
On Wednesday, president Josep Maria Bartomeu, CEO Oscar Grau and general manager Pep Segura returned to Amsterdam to finalise the agreement with Ajax and De Jong.
What you've all been waiting for... pic.twitter.com/gDE1mujMLF— FC Barcelona (@FCBarcelona) January 23, 2019
De Jong joined Ajax from Willem II in 2015 and subsequently progressed through the club's academy, making his first-team debut in 2017. He won his first international cap for the Netherlands last June and has already established himself as a key member of Ronald Koeman's team.
Before joining Barca, De Jong will try to help Ajax win a first Eredivisie title since 2013-14, while there is also a Champions League round of 16 meeting with Real Madrid around the corner.