Cook and stir ground beef in a skillet over medium heat with onion and garlic until the meat is completely browned, about 10 minutes. Drain excess grease.
Stir cream of mushroom soup, vegetable broth, vegetable juice cocktail, sherry, and Worcestershire sauce together in a slow cooker. Add beef mixture; stir in potatoes, corn, peas, carrots, mushroom pieces, celery flakes, salt, black pepper, marjoram, and thyme. Set cooker to Low, cover, and cook until vegetables are tender and sauce has thickened, about 8 hours. If preferred, set cooker on High and cook 4 hours.