Rinse the split peas under cold water and pick out any small stones. Place them in the slow cooker.
Add the chopped onion, sliced carrots, chopped celery, diced potatoes, and minced garlic to the slow cooker.
Pour in the vegetable broth. Stir in the dried thyme, bay leaves, salt, and black pepper.
Cover and cook on low for 7 to 8 hours until the split peas are soft and the vegetables are tender.
Remove the bay leaves. Stir the soup well to help the split peas thicken the broth slightly before serving.