He was also a diplomat (honorary consul for San Marino), a traveller (in Europe, the Balkans and North Africa), a flying buff who officiated at the first British air meeting at Doncaster in 1909, and a wireless pioneer who broadcast music from his own station long before radio was generally available; his claims regarding his own abilities and exploits, however, were usually exaggerated.

Le Queux mainly wrote in the genres of Romance, mystery, thriller, and espionage, particularly in the years leading up to World War I, when his partnership with British publishing magnate Lord Northcliffe led to the serialised publication and intensive publicising (including actors dressed as German soldiers walking along Regent Street) of pulp-fiction spy stories and invasion literature such as The Invasion of 1910, The Poisoned Bullet, and Spies of the Kaiser.

He wrote One day, during the five years I lived at the Hotel Cecil, a waiter brought me a card bearing the name of Broström, with an address in Stockholm.

A tall, middle-aged, clean-shaven Swede was ushered in, and handed me a letter of introduction from a friend, a certain Baroness Nernberg, who is one of the leaders of Society in the Swedish capital.

Briefly, it was that a friend of his, a certain Professor Afzelius (sic), at Abó University, had discovered in the original text of the Book of Ezekiel preserved in the Imperial Library at Petrograd a cipher message that gave the whereabouts of the concealed treasures from King Solomon's temple.

On the basis of the positive response to the cypher documents Le Queux approached Sir C. Arthur Pearson, the proprietor of the Standard newspaper for funding for the expedition to Jerusalem.

The newspaper's circulation increased greatly, and it made a small fortune for Le Queux, eventually being translated into twenty-seven languages and selling over one million copies in book form.

That same year he was elected the first President of the Hastings, St. Leonard's and District Radio Society, whose inaugural lecture was delivered on 28 April 1924 by John Logie Baird.

The latter contains, among other fantastic stories, the claim by Le Queux that he saw a manuscript in French written by Rasputin stating that Jack the Ripper was a Russian doctor named Alexander Pedachenko who committed the murders to confuse and ridicule Scotland Yard.

[13][14] Le Queux wrote 150 novels dealing with international intrigue, as well as books warning of Britain's vulnerability to European invasion before World War I:[15]