In a microwave-safe bowl, combine chocolate chips and sweetened condensed milk. Microwave in 30-second intervals, stirring in between, until melted and smooth.

Stir in the miniature marshmallows and M&M's until evenly distributed.

Pour the mixture into a greased baking dish and spread evenly.

Refrigerate for at least 2 hours or until set.

Cut into squares and serve.