Brown the ground beef and chopped onion in a large skillet over medium heat. Stir occasionally to ensure even cooking.
Drain any excess fat from the browned beef. This step helps reduce grease in your soup.
Transfer the beef and onions to a large pot or slow cooker. Add the taco seasoning and ranch dressing mix, stirring to combine.
Add the black beans, kidney beans, corn, tomatoes with green chilies, and chicken broth to the pot. Stir well to incorporate all the ingredients.
Simmer the mixture on low heat for 45 minutes to an hour if using a stovetop. For slow cooking, aim for 4-6 hours on low heat.