Heat the olive oil in a large skillet on the stove over medium-high heat. Add the onion to the pan and cook until softened, about 2 minutes.
Add the ground beef in the pan and cook until browned, crumbling with a spoon or spatula.
Add the garlic to the pan and cook, stirring, for 30 seconds. Remove the pan from the heat. Transfer the contents of the skillet to the slow cooker.
Add the bell pepper, chili powder, cumin, oregano, paprika, brown sugar, salt, black pepper, tomato paste, broth and diced tomatoes to the slow cooker. Stir.
Gently stir in the kidney beans and black beans.
Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours.
Serve chili with toppings as desired.