How to Cook a Boneless Top Sirloin Roast in a Slow Cooker

by Meg Jernigan

Roast beef and vegetables can be an elegant or casual meal.

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Boneless top sirloin roast is one of the leaner cuts of beef, and is typically broiled, grilled or roasted. If you decide to cook it in a slow cooker, the low heat and longer cooking time ensures that your dinner will be juicy and tender. Slow cooking can remove some of the flavors out of the beef however, and if done incorrectly, may leave you with a stringy, tasteless roast; combat a tasteless roast with bold seasonings and strong flavors. Use vegetables that can stand up to long cooking times for a true one-dish meal.

Step 1

Peel and cut up potatoes, onions and carrots or other root vegetables such as parsnips or turnips. Arrange the cut-up vegetables in the bottom of the slow cooker.

Step 2

Dissolve either vegetable or beef bouillon cubes in warm water and pour the liquid over the vegetables. Alternatively, pour in just enough fresh beef stock to cover the vegetables.

Step 3

Sear the sirloin roast over high heat in a heavy pan. Add a little peanut, vegetable or canola oil, heat the pan until the oil shimmers and carefully lay the roast in the pan. Let it cook for a couple of minutes, then turn it. Immediately after turning it, season the cooked side with salt and pepper, a commercial seasoning blend or your own section of herbs and spices. Sear and season the other side. Searing your roast helps seal in the juices, creating a tastier meal.

Step 4

Place the seared roast on top of the vegetables in the slow cooker and put the lid on. Cook for around six hours on high, or around eight hours on low.

Step 5

Take the roast out of the slow cooker, cover it loosely and let it rest for about 15 minutes. While the meat rests, use a slotted spoon to remove the vegetables. Transfer the cooking liquid to a saucepan and bring it to a slow boil. Mix a tablespoon or two of flour into a cup of cold water and whisk the flour and water mixture into the boiling liquid. Stir and cook until the gravy is as thick as you like it.

Step 6

Slice the meat and serve the vegetables and gravy on the side.

Items you will need

  • Root Vegetables
  • Bouillon Cube or Beef stock
  • Heavy Pan
  • Oil
  • Salt and Pepper
  • Slotted Spoon
  • Saucepan
  • Flour
  • Whisk


  • Before you sear the sirloin roast, cut slits in the meat every few inches with a sharp knife. Peel and thinly slice a clove of garlic, and press a slice into each slit. Alternatively, fill each slit with fresh herbs. If you’re pressed for time, don’t sear the meat. Searing adds color and flavor, but isn’t absolutely necessary. Coat the meat lightly with a little flour before searing it. The liquid in the slow cooker may thicken sufficiently from the flour, making it unnecessary to make gravy after the meat is cooked.


  • Test the meat’s temperature with a probe thermometer. The USDA recommends cooking beef roasts to an internal temperature of 145 F for medium-rare, 160 for medium and 170 F for well done. Also, you want to make sure the roast is fully thawed before you put it in the slow cooker. If the meat is frozen, the interior won’t cook at the same rate as the exterior. Don’t lift the lid to peek at the roast; opening the slow cooker will drop the temperature and add cooking time. Also, don’t overfill the slow cooker. It shouldn’t be more than 2/3 full.

Photo Credits

  • Jupiterimages/Comstock/Getty Images

About the Author

Meg Jernigan has been writing for more than 30 years. She specializes in travel, cooking and interior decorating. Her offline credits include copy editing full-length books and creating marketing copy for nonprofit organizations. Jernigan attended George Washington University, majoring in speech and drama.