Place the cubed watermelon into a blender.
Blend on high until the mixture is completely smooth and has a bright pink, uniform color, about 1 minute.
Pour the pureed watermelon into a mixing bowl.
Transfer the mixture to the freezer and freeze for at least 4 hours, stirring every 30 minutes for the first 2 hours to break up ice crystals and promote a smooth texture.
Once frozen and slightly firm, use a scoop or spatula to scrape and serve the sorbet. The texture should be icy but slightly chewy, with a vibrant pink appearance.