Australian marathon runner Liam Adams has said he "was in complete shock" when he discovered he had not qualified for this year's Paris Olympic Games.

Adams, 37, who competed at Olympic Games in Rio and Tokyo believed he had qualified for this year's event.

While Adams was not part of the 70-man list who completed a race in Olympic qualifying time, he believed his world ranking would allow him to join the 80-runner field. 

However, the remaining spots have been given to "universality places" which is for athletes who come from "under-represented National Olympic Committees" according to the International Olympic Committee.

"They are designed to increase the diversity of participating nations across the sports programme of the Olympic Games," the IOC states.

But Adams told ABC News he, and many others, believed the World Athletics would fill those remaining places based off world rankings instead.

"What ended up happening was I finished the qualification period in 74th position out of the 80," he told Charles Brice on News Breakfast.

"Through everything that I had read, through everything that Athletics Australia had read and even the other nations we were all under the impression that you finished in the top 80 and you'd be going to the Olympics.