In Belgium, the authority over cultural diversity policies resulting from immigration has been devolved from the central state to the regions since 1970. Consequently, Flanders and Francophone Belgium have progressively developed divergent policy tools. By describing the divergent evolution of Francophone and Flemish cultural diversity policies, our paper demonstrates the existence of a “Belgian Cultural Diversity Paradox”, namely the existence of more multicultural minority rights in the region that has most experienced electoral success by an extreme-right anti-immigrant party (Flanders), and a more colour blind and radical secular approach in the region where anti-immigrant politicization is barely a factor (Francophone Belgium). This finding is counter-intuitive because an important strand of immigrant policy research has emphasized the relationship between the politicization of immigration and restrictive immigrant citizenship rights. Our paper demonstrates that the different degrees of politicization of immigration in Flanders and Francophone Belgium cannot fully account for divergent cultural diversity policies. By insisting on the historical path dependency of the linguistic and religious cleavages in Belgium and their overlap, this paper offers an addendum to the politicization approach. The historical linguistic and religious differences of the Belgian regions clearly mediate the impact of the politicization of immigration on both sides of the linguistic border.