Slow Cooker Prime Rib Roast (Tender, Juicy & Foolproof)

Slow Cooker Prime Rib on a platter with thyme, roasted baby potatoes, and horseradish sauce.

Slow Cooker Prime Rib Roast (Tender, Juicy & Foolproof)

This Slow Cooker Prime Rib Roast delivers restaurant-quality results with a fraction of the effort. A generous kosher salt and pepper seasoning, a bold dijon-horseradish crust, and a long, low-temperature slow cook bring you perfectly juicy, medium-rare beef every time — no oven-babysitting required. A quick finish under the broiler builds that caramelized exterior crust that makes prime rib unmistakable. Let it rest, slice it thick, and serve with homemade creamy horseradish sauce for a holiday main course that will genuinely impress.

Prep Time20

Cook Time4

Resting time30

Total Time4 50

Course: Main Course

Cuisine: American

Diet: Gluten Free

Servings: servings

Calories: 660kcal

Author: Briana

Equipment

large slow cooker
oven safe meat thermometer

Ingredients

For the roast:

5 pound prime rib roast bone-in or boneless; also called beef ribeye roast or standing rib roast
5 teaspoons kosher salt 1 teaspoon Diamond Crystal per pound, see notes
1½-2 teaspoons coarse ground black pepper
1-2 tablespoons neutral oil as needed to seare

For the compound butter:

½ cup unsalted butter softened (1 stick)
10-12 cloves garlic minced (1 whole head)
1 tablespoon fresh thyme minced
1 tablespoon prepared horseradish
1 tablespoon Dijon mustard
kosher salt & black pepper to taste

For the slow cooker base:

1 cup beef stock
6-8 sprigs fresh thyme

Instructions

Season and dry brine:

Season the roast generously on all sides with kosher salt and coarse ground black pepper. For best results, place uncovered on a rack in the refrigerator for 12–14 hours. If short on time, season at least 1 hour before cooking and let come to room temperature.
5 pound prime rib roast, 5 teaspoons kosher salt, 1½-2 teaspoons coarse ground black pepper

Sear:

Heat a large skillet over medium-high heat and add oil. Sear the roast for about 4 minutes on the rib side, then 2–3 minutes on each remaining side until deeply browned all over. Remove from the skillet and set aside.
1-2 tablespoons neutral oil

Make the compound butter:

In a medium bowl, combine the softened butter, minced garlic, fresh thyme, horseradish, and dijon mustard with a pinch of salt and pepper. Mix well until a thick paste forms. Spread over the top and sides of the seared roast (not the bottom).
½ cup unsalted butter, 10-12 cloves garlic, 1 tablespoon fresh thyme, 1 tablespoon prepared horseradish, 1 tablespoon Dijon mustard

Slow cook:

Add the beef stock and thyme sprigs to the slow cooker. Place the roast ribs-side down. Cover and cook on LOW for 3–5 hours, until an instant-read thermometer inserted in the thickest part reads 5–8°F below your target doneness (see Notes for temperature guide).
1 cup beef stock, 6-8 sprigs fresh thyme

Rest and serve:

Transfer to a cutting board, tent loosely with foil, and rest for 20–30 minutes before slicing. Spoon drippings from the slow cooker over the slices to serve.

Notes

Optional broil finish: For a crispier fat cap, transfer the roast directly from the slow cooker to a foil-lined baking sheet and broil on high for 3–5 minutes before resting. Watch closely — it can go from golden to burnt quickly. Rest as directed after broiling.
Temperature guide (pull 5–8°F below target — roast continues to rise while resting):

- Rare: pull at ~120°F (finished ~125–127°F)
- Medium-rare: pull at ~125–130°F (finished ~130–135°F) — recommended
- Medium: pull at ~135°F (finished ~140–145°F)
- Well-done: not recommended for prime rib

Cook time guide (on LOW):

- 4–5 lb roast: approximately 3–4 hours
- 5–6 lb roast: approximately 3.5–4.5 hours
- 6–8 lb roast: approximately 4.5–5.5 hours All slow cookers run differently — always verify with a thermometer. Don't lift the lid early.

Salt note: Recipe is written for Diamond Crystal kosher salt. If using Morton's kosher salt, use approximately half the amount by volume.
Make-ahead: Season the roast up to 24 hours in advance and dry brine uncovered in the refrigerator. The compound butter can also be made up to 24 hours ahead and stored covered in the fridge — bring to room temperature before slathering.
Storage: Store leftover prime rib slices in an airtight container in the refrigerator for up to 4 days.
Reheating: Reheat gently in a 275°F oven, loosely covered with foil, until warmed through. Avoid the microwave — it overcooks the edges quickly.
Freezing: Freeze sliced leftover prime rib in an airtight freezer-safe container for up to 3 months. Thaw overnight in the refrigerator before reheating.
Serving suggestions: Pairs beautifully with creamy horseradish sauce, steakhouse creamed spinach, and old fashioned sweet potato casserole. For leftovers, try our prime rib sandwich with caramelized onions & arugula.

Nutrition