Preheat your oven to 350°F. Line a baking sheet with parchment paper.
In a large mixing bowl, cream together the softened butter, granulated sugar, brown sugar, and vanilla extract until smooth and fluffy.
Add the eggs one at a time, mixing well after each addition.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chocolate chips and M&M's until evenly distributed throughout the dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, leaving space between each cookie.
Bake for 10-12 minutes or until the edges are lightly golden. The centers may look slightly underbaked; they will continue to cook as they cool.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.