Line a 5-6 quart crockpot with parchment paper. Spread enough graham cracker crumbs to cover the bottom of the parchment paper evenly.
In a large bowl mix the chocolate cake mix according to the package. Once mixed stir in 1/4 cup of the chocolate chips and 1/2 cup mini marshmallows.
Spoon the batter on top of the graham crackers. Top with 1/4 cup chocolate chips and 1/2 cup of mini marshmallows.
Cover and bake on high for 2 to 2 1/2 hours or low for 3 - 4 hours. Cake is done when a toothpick inserted in the center comes out clean.
Carefully lift the cake out of the crockpot by the parchment paper and place on a cooling rack. While the cake is still hot top with the remaining marshmallows. Slice and serve!