Turn on the sauté function and add the olive oil to the pot. Once hot, add the stew beef cubes to the pot and sprinkle with the salt and pepper. Cook until browned on all sides and then remove the beef to a clean plate.
Add the onion, celery and carrots to the pot. Cook until the vegetables start to soften, about 5 minutes, stirring occasionally.
Stir in the garlic and cook, stirring, for 1 minute.
Pour in about 1 cup of the beef broth and stir, scraping up any bits that are stuck to the bottom of the pot.
Add the remaining beef broth, tomato paste, Worcestershire sauce, dried thyme, bay leaves, barley and browned beef along with any juices from the plate. Stir well.
Close the Instant Pot lid and set the steam release valve to the sealing position. Pressure cook on high pressure for 20 minutes. The Instant Pot will take about 15 minutes to reach pressure and then the cook time will start counting down.
When the cook time ends, allow the pressure to release naturally for 15 minutes by leaving the pot alone. Then quick release any remaining pressure by carefully moving the steam release valve to the venting position. Once all of the steam has escaped and the pin has dropped down, open the Instant Pot lid.
Remove and discard bay leaves. Adjust the seasonings, adding more salt and pepper if needed, to taste. Serve, garnished with fresh parsley.