Heat olive oil in a large skillet over medium-high heat. Season beef cubes with salt and pepper, then coat with flour.
Sear beef in batches until browned on all sides, about 2-3 minutes per side. Transfer to slow cooker.
Add potatoes, carrots, celery, onion, and garlic to the slow cooker.
In a bowl, whisk together beef broth, tomato paste, and Worcestershire sauce. Pour over ingredients in slow cooker.
Add bay leaves and thyme. Stir gently to combine.
Cover and cook on LOW for 8 hours or HIGH for 4 hours, until beef is fork-tender and vegetables are cooked through.
Remove bay leaves. Taste and adjust seasoning with additional salt and pepper if needed.
Serve hot, garnished with fresh parsley. Enjoy with crusty bread.