Prepare a baking sheet with parchment paper and set aside.
Place popped popcorn in a large mixing bowl.
In a saucepan melt butter. Once melted add in mini marshmallows and melt making sure to stir constantly. Once melted pour over popcorn and gently mix.
Once your popcorn is coated add it to your prepared baking sheet and add in M&Ms. Allow to cool then break popcorn into pieces and enjoy.