Pat the beef chuck roast dry and season generously with salt and pepper. Heat olive oil in a skillet over medium-high heat. Sear the roast on all sides until deeply browned, about 4-5 minutes per side, enhancing flavor and color. Transfer the seared beef to the slow cooker.
In the same skillet, add sliced onions, chopped celery, and minced garlic. Cook over medium heat, stirring occasionally, until the onions are translucent and fragrant, about 5 minutes. Add tomato paste and dried thyme, cooking for another minute to deepen the flavors.
Pour the vegetable mixture over the beef in the slow cooker. Add the chopped carrots and beef broth around the roast. Cover with the lid, set to low, and cook for 8 hours, until the meat is fall-apart tender and easily shreds with a fork.
Once cooked, carefully remove the beef from the slow cooker and transfer to a serving platter. Use two forks to shred the meat into thick, juicy strands, noting its melt-in-your-mouth texture.
Skim excess fat from the surface of the cooking liquid in the slow cooker. Turn the cooker to high and let the gravy simmer uncovered for 10-15 minutes, allowing it to thicken slightly and intensify in flavor.
Pour the thickened gravy over the shredded beef. Garnish with fresh herbs if desired and serve hot, with your favorite sides like mashed potatoes or roasted vegetables.
