In a mixing bowl, combine the graham cracker crumbs, sugar, and melted butter. Press the mixture into the bottom of a pie dish to form the crust.
Prepare the brownie mix according to the instructions on the box. Pour the brownie batter over the graham cracker crust.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Remove the pie from the oven and sprinkle the mini marshmallows evenly over the top. Return to the oven and bake for an additional 5 minutes, or until the marshmallows are golden brown.
Let the pie cool for a few minutes before slicing and serving.