The 29-year-old, who has 12 caps to his name, began his career in his native country with Lierse, where he won the Belgian title, before moving onto Dutch side Roda JC then Vitesse.
Speaking to Millwall's official site, Lions boss Mark McGhee said: "With the injury to Mark McCammon we are missing a target man of his type in the squad.
We stated that we are determined to cover all positions and this signing demonstrates how serious we are about that.
We have taken our time but we feel we have got a player of the experience and quality that will be required this season. With Noel Whelan, Neil Harris, Bob and the return to fitness of Richard Sadlier, I now feel we have a complement of strikers that gives us variety and depth."