Add the rinsed navy beans, vegetable broth, sliced carrots, diced parsnips, diced turnip, chopped onion, and minced garlic to the slow cooker.
Stir in the dried thyme, bay leaf, salt, and black pepper until everything is evenly distributed.
Cover and cook on low for 8 hours until the beans are soft and the vegetables are tender.
Remove the bay leaf and give the soup a gentle stir to thicken the broth slightly from the broken-down beans.
Taste and adjust salt or pepper if needed before serving.