Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.
In a large bowl, mix flour, cocoa powder, baking soda, and salt together.
In another bowl, beat butter, brown sugar, and granulated sugar until creamy.
Add eggs and vanilla to the butter mixture, beating well.
Gradually add dry ingredients to the wet mixture, mixing until combined.
Stir in the mint chocolate chips.
Drop tablespoonfuls of dough onto the prepared baking sheets.
Bake for 10-12 minutes or until cookies are set.
Let cookies cool on baking sheets for 5 minutes before transferring to wire racks to cool completely.