Heat the olive oil in a large skillet over medium-high heat. Add the beef cubes and brown on all sides for about 5 minutes. Transfer the beef to the slow cooker.
Add the mushrooms, onion, carrots, celery, and garlic to the slow cooker.
Pour in the red wine and beef broth. Stir in the tomato paste, thyme, bay leaves, salt, and black pepper until the tomato paste dissolves.
Cover and cook on low for 8 hours or until the beef is fork-tender.
Remove the bay leaves before serving.