Thomas Christiansen is keen to strengthen his squad during January with the Yorkshire giants currently sitting in sixth place in the Championship standings, and the head coach has acted by bringing in De Bock for an undisclosed fee.
De Bock leaves the Belgian side having made 153 appearances in all competitions, and the left-back has insisted that he could not turn down the opportunity to make the switch to English football.
The 25-year-old told the club's official website: "I'm very happy to be here and it feels like the next step in my career. I'm really looking forward to playing at this beautiful club in front of the beautiful fans at the stadium and atmosphere.
"I've heard a lot about Leeds United, I've spoken to players who play in England and I asked a few questions and everyone says the same thing - that it is a beautiful club and when I was younger I remember Leeds playing in the Premier League.
"It was a big decision I had to make, because I also have my wife and little boy, but when you have the chance come to England and being 25 now, I had to make the decision and I'm looking forward to playing in the most beautiful football country in the world."
De Bock could make his debut when Leeds travel to Portman Road to face Ipswich Town on Saturday afternoon.