John Tilleard was a solicitor of the City of London. He spent his free time on collect stamps and the study philately. He was a specialist of stamps issued by Prince Edward Island and British India. About the latter, he wrote Notes on the De La Rue Series of Adhesive Postage Stamps and Telegraph Stamps of India published in 1896.
On the Duke of Edinburgh's initiative, Tilleard met the Duke of York on 28 February 1893. He agreed to become George's advisor to help manage his stamp collection. George V's biographer, Harold Nicolson, commented that Tilleard was seen at the Duke of York's palace more often than Tanner who taught the future king law and constitutional knowledge.
After the accession of the Duke as King George V in 1910, Tilleard was named "Philatelist to the King" with a yearly 750 pounds salary. The next year the King made him a Member in the Royal Victorian Order (MVO) for his services to the King and philately.
In the history of the Royal Philatelic Collection, Tilleard was the principal force behind George V creating the most comprehensive collection of United Kingdom and Commonwealth stamps in the world. However, at the time of his death, the mounting was still to be done; performing this task was the main success of Tilleard's successor Edward Denny Bacon.
Member of the Philatelic Society, London, he served as honorary secretary from 1894 to 1913. He permitted the participation of two philatelist princes to the Society : Alfred, Duke of Edinburgh, brother of future King Edward VII, elected honorary president in 1890, and Alfred's nephew George, Duke of York.
In memory of Tilleard, the Royal Philatelic Society London created the Tilleard Medal, first awarded in 1920 to one (or two, if they are associated) members of the Society for the best philatelic display.