Season chuck roast with salt and pepper.

Heat a large skillet over medium-high heat; brown roast on all sides, about 4 minutes per side. Transfer roast to a slow cooker. Pour beef stock into the skillet, and bring to a boil while scraping the browned bits of food off of the bottom of the pan with a wooden spoon. Add broth and onions into slow cooker; cover and cook on Low for 5 hours.

Add potatoes, carrots, celery, and parsley. Cover and cook on Low until roast is tender and cooked through, 3 additional hours.