Heat olive oil in a large skillet over medium high heat. Add sausage and onion, and cook, stirring frequently, until sausage is browned, about 5-7 minutes, making sure to crumble the sausage as it cooks; drain excess fat.
Place sausage mixture into a 6-qt slow cooker. Stir in chicken stock, tomato sauce, diced tomatoes, beans, carrots, celery, garlic, basil, oregano and thyme; season with salt and pepper, to taste.
Cover and cook on low heat for 7-8 hours or high heat for 5-6 hours. Uncover and stir in pasta; cover and cook on high heat for an additional 30 minutes, or until tender.