Gather all ingredients.
Preheat the oven to 325 degrees F (165 degrees C).
Season brisket on all sides with salt and pepper and place in a glass baking dish. Cover with a layer of sliced onion.
Mix beer, chili sauce, and brown sugar together in a medium bowl. Pour over beef brisket. Cover the dish tightly with aluminum foil.
Bake in the preheated oven for 3 hours. Remove the aluminum foil and bake for an additional 30 minutes.
Let brisket rest and cool slightly before slicing and returning to the dish. Reheat in the oven with the sauce spooned over the sliced meat.
