[[Image:Fox-davies.jpg|thumb|400px|Cover of The Complete Guide to Heraldry (1929 edition) showing the Fox-Davies [[coat of arms] ]]Fox-Davies' writing on heraldry is characterised by a passionate attachment to heraldry as art, as history and also as law. He was something of a polemicist, and issued one of his most controversial works (The Right to Bear Arms) under a pseudonym ("X"). However, he always supported his arguments with specific historical and manuscript evidence.

He conducted a lifelong campaign against the bearing of coats of arms without lawful authority in accordance with the Law of Arms, whether that authority was a right recognised at the Visitations conducted by heralds between the 16th to 18th centuries or, more commonly, a right deriving from a specific grant entered in the records of the College of Arms. In support of this campaign, he produced a directory which attempted to list all living bearers of arms in England and Wales who could prove such authority, under the title Armorial Families. This served as an incentive to families who had not got such authority to regularise their position at the College of Arms and the size of the work increased considerably until its final edition in 1929, which remains the most comprehensive published record (the records of the College of Arms being largely unpublished) of post-Victorian heraldry in Britain. Many of the arms were illustrated with specially commissioned heraldic drawings, and Fox-Davies drew on this large resource when illustrating his more systematic treatises on heraldry.

The most lavish of these was The Art of Heraldry, which was originally conceived as an English translation of a German publication but transformed, in Fox-Davies' hands, into a largely original work specifically directed to the history, theory and practice of English heraldry, with illustrations in black and white and in colour throughout. Much of this material was re-used in a shorter, cheaper and more popular exposition of contemporary English heraldic practice, Complete Guide to Heraldry, which proved very successful and influential. Another even shorter guide was Heraldry Explained, but even this balanced a clear and didactic text with plentiful illustration.

Fox-Davies' emphasis on practical and officially authorised heraldry caused him to showcase mostly recent grants of arms. This was in contrast to the medieval emphasis of other scholars, of whom his most prominent critics were Oswald Barron, author of the celebrated article on heraldry in the 1911 edition of the Encyclopædia Britannica, and Horace Round.

Round, in an essay called "Heraldry and the Gent" (eventually published in his collection Peerage and Pedigree), ridiculed another thesis with which Fox-Davies was particularly associated, namely, that an English grant of arms was equivalent to a continental patent of nobility, and that, not only were all English armigers to that extent noblemen as well as gentlemen (if male), but that no one without an official right to bear a coat of arms could claim to be a gentleman at all.

Fox-Davies' influence on English heraldry continued long after his death in 1928, not least because of his lawyerly insistence on backing his opinions with solid evidence, and because of the continuing popularity of his books with the general public and with expert heraldists alike. One of his admirers in the next generation was John Brooke-Little, Clarenceux King of Arms and founder of the Heraldry Society, who edited a new edition of The Complete Guide to Heraldry and in many ways propagated similar, albeit somewhat less aggressively expressed, ideas.

Fox-Davies did not become a herald or pursuivant at the College of Arms, but he served as Gold Staff Officer at the Coronation of George V.

Fox-Davies was brought up at Coalbrookdale, Shropshire. His paternal family (Davies) was of Welsh origin. His maternal grandfather was John Fox of Coalbrookdale.

Fox-Davies was educated at Ackworth School, Yorkshire. He does not appear to have received a university education, but was called to the Bar by Lincoln's Inn.

As a barrister, he practised on the South Eastern Circuit, at the Old Bailey, and at the Surrey and South London Sessions. He also prepared printed cases for peerage cases in the House of Lords.

In addition to his writing on heraldry, he published a number of works of fiction.

He was a Conservative in politics, and unsuccessfully stood for election as Member of Parliament for Merthyr Tydfil in 1910, 1923 and 1924. He was, however, elected as a member of Holborn Borough Council in London.

He married in 1901 Mary Crookes, by whom he had one son and one daughter. He lived at Warwick Gardens, Kensington, London, and had chambers at 23 Old Buildings, Lincoln's Inn.