Season the beef cubes with salt and pepper. Place the bacon in a large skillet over medium heat and cook until crisp. Remove the bacon and set it aside, leaving the drippings in the pan.
Add the beef to the skillet in batches and brown on all sides. Transfer the browned beef to the slow cooker.
Add the onion and garlic to the same skillet and cook for two minutes. Stir in the flour and tomato paste, then pour in the red wine. Scrape the bottom of the pan and let the mixture simmer for one minute before transferring everything to the slow cooker.
Add the carrots, parsnips, potatoes, mushrooms, thyme, bay leaves, beef broth, and cooked bacon to the slow cooker. Stir to combine.
Cover and cook on low for 8 hours. Remove the bay leaves before serving and sprinkle with fresh parsley.