Heat a large skillet over medium-high heat and stir in ground beef. Cook and stir until beef is crumbly, evenly browned, and no longer pink, about 7 minutes. Drain and discard any excess grease.
Combine ground beef, kidney beans, diced tomatoes, tomato sauce, onions, bell pepper, garlic, chili powder, cayenne pepper, salt, and black pepper in a slow cooker. Cover and cook on Low for 10 hours, or High for 4 hours.