Preheat a skillet over medium-high heat. Add a bit of oil, then brown the beef chunks in batches until each piece develops a deep golden crust, about 5-7 minutes per batch. Transfer the browned beef to the slow cooker.
In the same skillet, sauté diced onions until they become translucent and fragrant, about 4-5 minutes, scraping up browned bits from the bottom. Transfer the onions to the slow cooker.
Add chopped carrots and celery to the slow cooker, along with minced garlic, dried thyme, salt, and pepper. Pour in beef broth, diced tomatoes with their juice, and tomato paste. Stir gently to combine all ingredients.
Cover the slow cooker with its lid and set it to cook on low for 8 hours. During this time, the beef will become tender and the flavors will meld, filling your home with a warm, savory aroma.
Once cooked, turn off the slow cooker and carefully open the lid. Check the beef—should be meltingly tender—and vegetables should be soft. If desired, adjust seasoning with additional salt and pepper.
Serve the beef stew hot, spooned into bowls with a generous ladle of the rich gravy, and enjoy the hearty, melt-in-your-mouth texture of this classic dish.
