Place the Italian sausage in the slow cooker and break it into small pieces with a spoon.
Add the drained white beans, chicken broth, diced tomatoes with their juices, chopped onion, and minced garlic.
Sprinkle in the dried oregano, dried basil, salt, and black pepper.
Stir everything together until the ingredients are evenly combined.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the sausage is fully cooked and the flavors have blended.
Ladle the soup into bowls and top with fresh basil leaves before serving.