Preheat your oven to 350°F (175°C).
In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add in the eggs, one at a time, mixing well after each addition, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt.
Gradually mix the dry ingredients into the wet mixture until just combined.
Fold in the chocolate chips and M&M's until evenly dispersed throughout the dough.
Scoop tablespoon-sized portions of dough onto ungreased baking sheets, leaving space between each ball.
Bake for 10-12 minutes, or until the edges are set but the centers are still soft.
Allow the cookies to cool on the baking sheets for a few minutes before transferring them to wire racks.
Enjoy your freshly baked cookies warm or at room temperature.