The Netherlands international had long been linked with a move to the Bundesliga side, and has now completed the transfer.
Die Fohlen have been in the market for attacking reinforcements since the departure of Marco Reus to Borussia Dortmund, and coach Lucien Favre has now got the new striker he had set his sights on.
"We are very pleased that it's now a done deal after all, and that Luuk will be able to travel to our training camp in Tegernsee on Friday," Gladbach sporting director Max Eberl commented.
"In Luuk, we have secured the services of a very talented striker who has already plenty of international experience under his belt with Twente and the Dutch national side, despite his tender age of 21."
De Jong is a product of the De Graafschap youth academy, and joined Twente in the summer of 2009. He had since developed into a key player at the Eredivisie outfit, netting 39 goals in 75 league appearances.
The Netherlands international had also attracted the interest of Newcastle United, but the Premier League side pulled out of the race for De Jong's signature due to Twente's hefty asking price for the striker.
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