Place the rinsed split peas, diced ham, chopped onion, sliced carrots, and sliced celery into the slow cooker.
Pour in the chicken broth and add the dried thyme and bay leaf.
Season with salt and black pepper, then stir everything together.
Cover and cook on low for 7 to 8 hours until the peas are soft and the soup has thickened.
Remove the bay leaf, give the soup a final stir, and serve.