As a 14-year-old student at King Edward VII School in Johannesburg, Arnheim was picked to join the "Quiz Kids" team of five capped and gowned teenagers, appearing on South Africa's Springbok Radio,[4] and of which he became a stalwart member, "retiring" at the age of eighteen.

[4] Besides his academic pursuits (including teaching numerous undergraduates) he engaged in student politics, being elected a member of the Junior Combination Room committee and College NUS secretary, in which capacity he represented the College at several national conferences, including one in 1968 at which he proposed a widely supported motion to the effect that the English A-Level system was unduly narrow and should be broadened.

In 1969, at the age of 25, Arnheim was awarded his Cambridge Ph.D. His doctoral dissertation was subsequently published by the Oxford University Press under the title The Senatorial Aristocracy in the Later Roman Empire.

[5] In the meantime Arnheim was elected a Fellow of St John's College, Cambridge, where he did a great deal of teaching for a number of colleges while researching his next book, Aristocracy in Greek Society (1977),[6] which he was invited by Professor Howard Hayes Scullard to write as part of the prestigious Thames & Hudson series, Aspects of Greek and Roman Life.

Professor Michael Arnheim of the University of the Witwatersrand thinks this is entirely wrong; Christians ought to take the gospels au pied de la lettre, and then face some highly inconvenient facts: Jesus did not literally fulfil Jewish expectations of the Messiah and so was not the Messiah; many of the stories about him are plainly false or internally inconsistent; he himself does not exemplify the humility and above all the love even of enemies that he demanded; his ethical teaching is so unrealistic that it was bound to make Christians into the hypocrites that they are.

Despondent about the future of South Africa, Arnheim returned to Britain, where he was called to the Bar by Lincoln's Inn in 1988,[4] and went into practice as a London barrister specializing in civil litigation, with a certain amount of criminal defence on the side, notably the Cardiff Prison Riot trial in 1992.

Arnheim, in 1992, was an early voice in the legal profession to adamantly insist that a person could face criminal liability for knowingly concealing their HIV-positive status from a sexual partner.

From early on in his practice at the Bar, Arnheim wrote articles in favor of clients' being allowed to come direct to a barrister, thus avoiding the additional expense of having to be referred by a solicitor.

His pleas fell on deaf ears until the idea was taken up in a hard-hitting report by the Director of Fair Trading, Sir John Vickers, published in 2000.

Arnheim contended that the reason the Western Empire fell was that the central government in the West was sapped from within by the senatorial aristocracy, who now again dominated the top administrative posts while building up their own countervailing local power through the spread of large estates.

The same rise of the senatorial aristocracy did not occur in the Eastern half of the Empire, which therefore survived for another thousand years, albeit in a gradually shrinking state.

In 1994 Arnheim was invited to edit a volume of essays on the Common Law in the prestigious Dartmouth series, and published in the US by New York University Press.

Arnheim was delighted to be asked to write the U.S. Constitution for Dummies (2009)[20] as part of the well-known Wileys series of books with their distinctive black-and-yellow covers.