Preheat oven to 350°F. Line 9x13-inch pan baking with parchment paper. Grease and set aside.
In a large saucepan, melt butter and chocolate over medium-low heat. Once melted, add sugar and brown sugar. Stir to combine. Remove from heat.
Transfer batter to the bowl of a stand mixer with a paddle attachment. Add eggs one at a time, making sure each egg is fully incorporated before adding the next.
Whisk together flour, cocoa powder, and salt. Alternate adding dry mixture and Guinness to the batter. Starting and ending with the dry mixture. Fold in chocolate chips.
Pour into prepared pan. Bake for 25-30 minutes until toothpick inserted in the center of the brownie comes out clean. Let cool on rack.