In a large pot, brown the ground beef over medium heat until fully cooked. Drain excess fat.
Add chopped onion and minced garlic to the pot; sauté until onions are translucent.
Stir in chili powder and cumin; cook for 1 minute to release the spices' flavors.
Add diced tomatoes (with juice), kidney beans, black beans, and corn to the pot.
Season with salt and pepper to taste, then stir well.
Bring the mixture to a boil, then reduce heat to low.
Cover and let simmer for 20-25 minutes, stirring occasionally.
Taste and adjust seasonings as needed.
For a thicker chili, let it simmer uncovered for the last 5-10 minutes.
Serve hot, garnished with your choice of toppings like cheese or cilantro.