Cover the slow cooker with the lid and cook on LOW for 4 to 5 hours, or on HIGH for 2 to 3 hours, until the pork tenderloin is very tender and reaches an internal temperature of at least 145°F (63°C) when checked with an instant-read thermometer at the thickest part.
Once done, transfer the pork tenderloin to a cutting board and let it rest for about 5 minutes. While it rests, give the sauce in the slow cooker a quick stir to combine any separated juices into a smooth, savory gravy.
Slice the pork tenderloin into 1/2-inch thick medallions. Arrange the slices on a serving platter or individual plates and spoon the warm onion-mushroom gravy over the top. Serve immediately with your favorite sides.
Variations & Tips
For a slightly richer flavor, you can substitute beef broth for the water (keep the same amount) or add 1 tablespoon of Worcestershire sauce to the soup mixture—this will deepen the savory notes without adding any extra steps. If you prefer a lighter sauce, use a condensed cream of celery soup instead of cream of mushroom.
To add a touch of sweetness, scatter 1 small sliced onion or 1/2 cup sliced carrots around the pork before pouring on the soup mixture; they’ll soften into the sauce as it cooks. If your tenderloin is on the larger side (closer to 2 pounds), plan on the longer end of the cooking time and confirm doneness with a thermometer.
Food safety tips: Always keep raw pork refrigerated until you’re ready to cook, and avoid letting it sit at room temperature for more than 30 minutes. Use a dedicated cutting board and knife for raw meat, and wash them (and your hands) thoroughly with hot, soapy water before handling other ingredients. The USDA recommends cooking pork to a minimum internal temperature of 145°F (63°C) followed by a short rest; in a slow cooker, the meat will often go higher, which is fine for tenderness. Refrigerate leftovers within 2 hours in shallow containers and use within 3 to 4 days, reheating until hot and steaming before serving.
