Season the beef with salt and pepper.
In a large skillet over medium-high heat, add 1 tablespoon of oil and heat for one minute. Add the beef in batches and brown on all sides. Transfer the beef to the slow cooker and continue cooking the remaining beef, adding more oil as needed, until it is all browned.
To the slow cooker, add the mushrooms, carrots, garlic, potatoes, onions, beef broth, wine, tomato paste, and thyme. Stir well to evenly distribute.
Then, add the barley and bay leaves, stirring to combine.
Cover the slow cooker and cook on low for 6 to 8 hours.