Heat the olive oil in a large skillet over medium-high heat. Add the beef stew meat and brown on all sides for about 5 minutes. Transfer the meat to the slow cooker.
Add the onion and garlic to the same skillet and cook for 2 minutes until softened. Stir in the tomato paste and cook for another minute.
Transfer the onion mixture to the slow cooker. Add the carrots, parsnips, potato, pearl barley, beef broth, thyme, salt, and black pepper.
Stir everything together, cover the slow cooker, and cook on low for 7 to 8 hours or on high for 4 hours until the beef is tender and the barley is cooked through.
Taste and adjust salt and pepper if needed before serving.