In a 2 qt. slow cooker: place cranberries, sugar and orange juice; mix/stir.
Cover and slow cook on high for 2 hours.
Remove lid and stir.
Leave lid off and cook uncovered for ~1 more hour or until desire consistency (don't worry if it looks watery, it's going to thicken up as it cools . For a quick tip: put the sauce in the refrigerator and it will thicken faster). Best served cool.
Transfer to a serving bowl or airtight container.