Generously season the chuck roast with salt and pepper on all sides.
Heat olive oil in a large skillet over medium-high heat. Sear the roast on each side until nicely browned, about 4–5 minutes per side.
Transfer the seared roast to your slow cooker.
In the same skillet, sauté the chopped onion and minced garlic for 2–3 minutes until fragrant and softened. Add them to the slow cooker.
Arrange the chopped carrots, parsnips, and potatoes around the roast in the slow cooker.
In a small bowl, whisk together the beef broth, red wine (if using), tomato paste, Worcestershire sauce, thyme, and bay leaves. Pour this mixture over the roast and vegetables.
Cover and cook on low for 8–10 hours or high for 4–6 hours, until the meat is fork-tender and the vegetables are fully cooked.
Remove the thyme sprigs and bay leaves before serving.