Gather the ingredients. Preheat the oven to 350 degrees F (175 degrees C).
Place sweet potatoes in a 6x10-inch shallow baking dish. Drizzle with orange juice and set aside.
Mix together flour, sugar, cinnamon, and salt in a medium bowl until combined.
Cut in margarine with 2 knives or a pastry blender until mixture resembles coarse crumbs; sprinkle evenly over sweet potatoes.
Bake in the preheated oven for 30 minutes.
Remove casserole from the oven and turn on the broiler. Sprinkle marshmallows evenly over the top of casserole.
Cook under the broiler until marshmallows are puffed and golden brown.
