Heat sugar and 1 cup water in a small pot until sugar dissolves. Add 1 cup bing cherries, bring to a boil and boil until the cherries begin to soften, about 2 to 3 minutes. Set aside to cool.
Strain cooled bing cherry syrup into a large pitcher, pressing on the cherries to release their juice. Add lemon juice and cold water. Stir in remaining cherries. Pour over ice and garnish with lemon slices and fresh mint.