Brown the ground beef in a skillet over medium heat until no pink remains. Drain excess fat and transfer the beef to the slow cooker.
Add the chopped onion, minced garlic, kidney beans, black beans, pinto beans, diced tomatoes, and beef broth to the slow cooker.
Stir in the chili powder, cumin, salt, and black pepper until everything is evenly combined.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the onions are soft and the flavors have blended.
Ladle the chili into bowls and top each serving with shredded cheddar cheese.