Place beans in a large pot or bowl. Cover with water 2 inches above beans and soak for 8 hours (or overnight). Drain beans.
Transfer soaked beans to slow cooker insert.
Brown the sausage in a large skillet or Dutch oven over medium-high heat until no longer pink. Use a wooden spoon to break up the meat as it cooks. With a slotted spoon, remove the sausage to a paper towel-lined plate; reserve the drippings in the pan.
Saute carrots, celery, onion, and garlic in the sausage drippings until starting to soften, about 8-10 minutes. Transfer vegetables to the slow cooker.
To the slow cooker, add the broth, cooked sausage, salt, pepper, tomatoes, and bay leaves. Cover and cook on HIGH for 4-5 hours or on LOW for 8-10 hours, or until the beans and vegetables are tender. Discard bay leaves. Taste and season with additional salt and pepper, if desired. Ladle into bowls, garnish with fresh herbs, and serve.