Cook the Beef:
In a large soup pot or Dutch oven, brown the ground beef over medium heat. Break it up into small pieces as it cooks. Once browned, drain any excess grease.
Sauté the Onion:
Add the diced onion to the pot with the beef and cook until softened, about 3–4 minutes.
Combine Ingredients:
Stir in the black beans, kidney beans, corn, diced tomatoes, Rotel, taco seasoning, and ranch seasoning. Mix well.
Add Liquid:
Pour in the beef broth or water, stirring to combine. Bring the soup to a gentle boil.
Simmer:
Reduce the heat to low, cover, and let the soup simmer for 20–25 minutes, stirring occasionally to let the flavors meld together.
Serve:
Ladle the soup into bowls and top with your favorite garnishes.