Set the Instant Pot to sauté mode and add the olive oil. Once hot, add the beef and cook until browned on all sides, about 4 minutes.
Add the onion, carrots, celery, and mushrooms. Stir and cook for 3 minutes until the vegetables begin to soften.
Stir in the garlic and cook for 30 seconds. Turn off sauté mode.
Add the pearl barley, beef broth, thyme, bay leaves, salt, and pepper. Stir to combine.
Secure the lid and set the Instant Pot to manual high pressure for 25 minutes. Allow a natural pressure release for 10 minutes, then quick release any remaining pressure.
Remove the bay leaves. Stir in the fresh parsley before serving.