Season the beef with salt and pepper. Heat a large skillet over medium-high heat and brown the beef in batches until it develops color on all sides. Transfer the beef to the slow cooker.
Add the carrots, potatoes, parsnips, onion, and garlic to the slow cooker. Stir in the tomato paste and thyme until everything is coated.
Pour the beef broth over the mixture and tuck in the bay leaves. Cover and cook on low for 8 hours.
In a small bowl, whisk the flour with 2 tablespoons of water to make a slurry. Stir the slurry into the stew and cook on high for 20 more minutes until the broth thickens.
Remove the bay leaves before serving.