Cut the watermelon into cubes, removing any seeds and rind. You should have about 4 cups of cubed fruit.
Add the watermelon cubes and fresh mint leaves to a high-speed blender. Blend on high for 30-45 seconds until completely smooth and the mint is fully incorporated.
Taste the juice and add lime juice if desired for extra brightness and tang. Blend for another 10 seconds to combine.
For smooth juice, pour through a fine-mesh sieve set over a pitcher, pressing gently with a spoon to extract all liquid. For pulpy juice, pour directly into glasses.
Serve immediately over ice, garnished with fresh mint sprigs and small watermelon wedges. Store any leftovers in the refrigerator in a sealed container for up to 3 days.
