Add the cooked Italian sausage to the bottom of your slow cooker.
Stir everything together until well combined. Season however you like, if desired, keeping in mind the sausage and marinara already add plenty of flavor.
Cover and cook on LOW for 6 hours or HIGH for 2–3 hours, allowing the flavors to blend.
About 20 minutes before serving, add the cubed cream cheese, chopped spinach, and dry ditalini pasta.
Stir well, cover again, and cook for an additional 20 minutes, or until the pasta is tender and the cream cheese is fully melted.
Give the soup a final stir to ensure everything is evenly combined. Serve warm and enjoy!