Cut off both ends of the zested orange, and cut orange in half. Peel halves and remove the white core.
Place orange sections and cranberries in a food processor. Pulse until orange is mostly pulp, using roughly 5 three-second pulses.
Combine the orange-cranberry mixture, zest, sugar, and water in a medium saucepan. Bring to a gentle boil and simmer, stirring frequently, for 15 minutes. Let marmalade cool.
Pour marmalade into a glass jar with a tight-fitting lid. Chill completely in refrigerator before serving.