In a 4.5- to 6-L slow cooker, stir together meatballs, onion, garlic, carrots, celery, diced tomatoes, red kidney beans, tomato paste, chili powder, cumin, salt and pepper.
Cover and cook on LOW until flavours are blended, chili is thickened and meatballs are tender, about 7 hours. Add corn and cook on HIGH until mixture is steaming hot and corn is tender, about 7 min. Top with cilantro.
No slow cooker? Place all the ingredients in a large pot on the stove and cook over medium-high heat for about 35 minutes.