Combine the sugar and ¼ cup water in a small saucepan. Cook over medium heat, stirring often, until the sugar has completely dissolved, 1 to 2 minutes. Let it cool.
In a large pitcher or punch bowl, combine the Campari, gin, orange juice, and sugar syrup; chill for up to 12 hours. Just before serving, add the club soda, pomegranate seeds, and orange. Serve over ice.