In a large pot or Dutch oven, brown the ground beef with the chopped onion over medium-high heat. Drain off any excess grease.
Stir in the ranch seasoning mix, taco seasoning mix, diced tomatoes, black beans, pinto beans, corn, and beef broth.
Bring the soup to a boil, then reduce heat and simmer for at least 20 minutes, or until flavors have melded. For a richer flavor, simmer longer.
Serve hot with your favorite toppings.
Notes
For a slow cooker version, brown beef and onion on the stovetop, then transfer to a slow cooker with all other ingredients. Cook on low for 6-8 hours or high for 3-4 hours.
This soup is a great make-ahead meal and freezes well.
Adjust the amount of seasoning mix to your preference.