How long do you cook sliced roast beef in a crock pot?

You should never cook sliced roast beef in a crock pot. Slow-cooking sliced roast beef in a crockpot is not a safe method of preparation. Instead, sliced roast beef should be heated to a safe temperature of 165°F (74°C) before serving, such as by warming in the oven, on the stove, or in a microwave.