In a large skillet over medium-high heat, brown the ground beef with diced onion and minced garlic until the meat is fully cooked and no longer pink, about 8-10 minutes. Drain any excess fat.
Transfer the cooked beef mixture to your slow cooker. Add kidney beans, crushed tomatoes, tomato sauce, beef broth, chili powder, cumin, paprika, salt, and pepper. Stir everything together until well combined.
Cover and cook on LOW for 3-4 hours or on HIGH for 2-3 hours, stirring occasionally if possible.
About 30 minutes before serving, stir in the uncooked elbow macaroni. Make sure the pasta is fully submerged in the liquid. Cover and continue cooking until the pasta is tender.
Once the macaroni is cooked, stir in half of the cheddar and Monterey Jack cheese until melted and creamy.
Serve hot in bowls, topped with the remaining cheese. Add your favorite toppings like sour cream, green onions, or jalapeƱos if desired!