Heat a large pan over medium-high heat. Cook and stir ground venison with onion in the hot pan until browned and crumbly, 5 to 7 minutes.
Stovetop Option: Transfer cooked venison and onion into a large pot over medium heat. Stir in tomato sauce, diced tomatoes, chili beans, bell peppers, chili powder, cumin, salt, brown sugar, oregano, ground black pepper, cayenne pepper, and garlic. Bring to a boil; reduce heat to low and simmer for 1 1/2 hours.
Slow Cooker Option: Transfer cooked venison and onion into a slow cooker. Stir in tomato sauce, diced tomatoes, chili beans, bell peppers, chili powder, cumin, salt, brown sugar, oregano, ground black pepper, cayenne pepper, and garlic. Cover and cook on Low for 8 to 10 hours.
Notes
Too spicy? Pair this chili with sour cream and saltines. Reduce or remove the cayenne pepper if you haven't already added it.
Leftovers? Keep them in the fridge for up to a week or freeze for 3 months in airtight containers.
Too mild? Try adding a jalapeño or kick up the cayenne powder. Another option if you want a smokey flavor is to add chipotles in adobo sauce.
No venison? No problem! Just swap it out for ground beef and be sure to drain excess fat after browning.