Layer the onions, potatoes, and carrots into the bottom of a large Dutch oven. Place the brisket on top of the vegetables.
Mix the beef broth, onion soup mix, ketchup, and ginger ale in a bowl, and pour it over the brisket and vegetables. Bring to a boil over high heat, cover, and reduce heat to a simmer.
Simmer the brisket until tender, about 2 1/2 hours.
