Combine grape juice and pectin in a large pot over medium-high heat. Bring to a boil, and stir one minute at a rolling boil. Stir in sugar for a few minutes to completely dissolve. Remove from heat.
Ladle the hot jelly into sterile jars, leaving 1/2 inch of space at the top. Wipe rims of jars with a clean dry cloth. Cover with a lid and ring to seal. Let stand 24 hours at room temperature, then refrigerate. Jelly may take up to a week to set. Once set, it is ready to serve. Store in the refrigerator for up to three weeks, once set.
Cook's Note: If canning for long term storage, process in a hot water bath for 10 minutes, or contact your local extension for processing times in your area. Processing times may vary based on sugar content and altitude.