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.

[1] The defending champion was Ryan Cochrane of Canada.

[2] This event was a timed-final where each swimmer swam just once.

[3] Prior to this competition, the existing world and Pan Pacific records were as follows: All times are in minutes and seconds.

[4] Only two swimmers from each country was classified in the award ranking.