Preheat your oven to 350°F (175°C).
In a large bowl, cream the softened butter, granulated sugar, and brown sugar together until light and fluffy.
Add the eggs, one at a time, mixing well between each addition, then stir in the vanilla extract.
In a separate bowl, sift together the flour, cocoa powder, baking soda, and salt.
Gradually add the dry mixture to the wet ingredients, mixing until just combined.
Fold in the chocolate chips and M&Ms until evenly distributed.
Drop tablespoon-sized portions of dough onto a lined baking sheet, spacing them at least 2 inches apart.
Bake for 10-12 minutes or until the edges are set but the centers look slightly underbaked.
Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.