In a pot bring 1 cup sugar and 1 cup water to a boil.
Add cranberries and bring back to a boil. Reduce heat to medium-low and cook for 15 minutes.
Add diced mango to cranberries and cook for another 5 minutes.
Transfer cranberry mango sauce into a dish with a cover. Cover and let it cool to room temperature. After it's cooled store in the refrigerator until ready to use.