The 2018 Sydney SuperNight 300 was a motor racing event for the Supercars Championship, held on the weekend of 3–4 August 2018. The event was held at Sydney Motorsport Park in Eastern Creek, New South Wales and consisted of one race, 300 kilometres in length. It was the tenth event of sixteen in the 2018 Supercars Championship and hosted Race 21 of the season.

The 2018 Supercars Championship was an FIA-sanctioned international motor racing series for Supercars. It was the twentieth running of the Supercars Championship and the twenty-second series in which Supercars have contested the premier Australian touring car title. Teams and drivers competed in thirty-one races at sixteen venues across Australia and New Zealand for the championship titles. Scott McLaughlin won his maiden title at the final race in Newcastle, while Red Bull Holden Racing Team won the Teams Championship at Pukekohe.