In a large bowl, combine ground beef, breadcrumbs, Parmesan, parsley, egg, garlic, salt, and pepper.
Mix until well combined, but do not overmix.
Shape the mixture into meatballs, about 1 to 1.5 inches in diameter.
Place the meatballs in the bottom of the crockpot.
Pour marinara sauce over the meatballs, ensuring they are well coated.
Cover the crockpot with the lid.
Set the crockpot to low for 6 hours or high for 3 hours.
Check the meatballs for doneness; they should reach an internal temperature of 160°F.
Once cooked, garnish with fresh parsley before serving.
Serve with your choice of pasta, bread, or alone for a delightful meal.