The men's 800 metre freestyle competition at the 2018 Pan Pacific Swimming Championships took place on August 12 at the Tokyo Tatsumi International Swimming Center. The defending champion was Ryan Cochrane of Canada. This event was a timed-final where each swimmer swam just once. Early heat was swum at the end of the preliminary heats on that day from slowest to fastest. The fastest timed final heat was swum with the finals.