Cook beef and onion in a large skillet over medium-high 8-10 minutes until beef is browned with no pink and onion softened. Add garlic; cook another minute until fragrant and drain excess fat.
Transfer beef mixture to slow cooker.
Add beer, beans, tomatoes, tomato paste, chili powder, cumin, paprika, salt, and pepper; stir well.
Cover; cook on LOW 6-8 hours or HIGH 3-4 hours, stirring occasionally if possible.
Adjust seasoning to taste; serve hot with favorite toppings such as cheese, sour cream, and green onions.