Preheat the oven to 400 degrees F (200 degrees C).
Meanwhile, put cranberries in a small bowl and pour boiling water over them to cover. Let stand 15 minutes until plump; drain.
At the same time, slice off top rind of wheel of Brie. Put Brie in a pie plate.
Bake in the preheated oven until Brie is warmed through, about 15 minutes. Top with orange marmalade, cranberries, walnuts, and mint (if using).
