He rode for the Aldershot Shots, the Wimbledon Dons and the Southampton Saints.
Mardon began riding at the Aranui Speedway in Christchurch in 1949, the same track that would later start the career of six time World Champion and fellow Christchurch native Ivan Mauger.
He moved to England in 1951 and joined the third division team, Aldershot.
He qualified as second reserve for the 1951 World Final.
The following year he transferred to the Wimbledon team. He rode in the 1953 World Final and finished in 3rd place.
In 1954 Mardon was one of the highest individual points scorers in the National League.
He rode in the World final again and he won the Brandonapolis at Coventry.
Later in the year he married Valerie Moore, the sister of Ronnie Moore.
At the beginning of 1955 he decided to retire and live in New Zealand.
After a four year break Southampton persuaded him to return to British speedway in 1959.
He rode the Saints for a year and he qualified for the World final.