Combine rhubarb and sugar in a large bowl; toss to coat. Let stand 10 minutes or until natural juices form.
Transfer the rhubarb to a medium saucepan and heat at medium heat; stirring often. Continue cooking and stirring until mixture bubbles and softens.
Remove from heat and immediately add orange marmalade. Stir until thoroughly combined. Store in a sealed container in the refrigerator.
