Born in August 1873, Bertram was the son of Halford Mills of Paddington, London, an undertaker and the owner of the Reformed Funeral Company, a coach building works and the Undertakers Journal. Bertram was brought up on two small farms at Chalfont Saint Giles (which his father owned for the purpose of sending his horses there to rest), where he developed his passion for horseback riding.
His troupe were the last to perform with live animals on the Drury Lane Theatre stage. Halford Mills was described as a "pioneer of embalming". Within a year he was driving a four-in-hand from London to Oxford wearing a cornflower in his morning coat, for which he later became recognised.
He continued working for the family firm until the outbreak of World War I when he joined and served with the Royal Army Medical Corps, rising to the rank of Captain.
On leaving the army he became interested in the "Wilkins and Young Circus". He made a wager with a friend that he could form a circus company and within a year be as good as they were.
He did just that and thus the "Bertram Mills International Circus" was formed. The circus very quickly became a household name and the annual Christmas event became especially well-known.
He made a point of inviting orphans to see the shows for free.
By 1930 (its heyday would last for the next thirty years, when it was the best and most famous live show) he had inaugurated a touring circus which became unique amongst British circuses, always appearing at Olympia for the Christmas season. The guest lists indicate the show"s renown. The Royal family, who were great supporters, attended every year, and Winston Churchill and similar dignitaries were also annual guests.
