His posthumously published The Miracle of Theism: Arguments For and Against the Existence of God (1982)[1] has been called a tour de force in contemporary analytic philosophy.

[7][5] Mackie graduated from the University of Sydney in 1938 after studying under John Anderson, sharing the medal in philosophy with Harold Glass.

Mackie received the Wentworth Travelling Fellowship to study greats at Oriel College, Oxford, where he graduated with first-class honours in 1940.

[5] During the Second World War Mackie served with the Royal Electrical and Mechanical Engineers in the Middle East and Italy, and was mentioned in dispatches.

[10] This personal style is exemplified by the following words from the preface to Ethics: Inventing Right and Wrong: I am nowhere mainly concerned to refute any individual writer.

I believe that all those to whom I have referred, even those with whom I disagree most strongly, have contributed significantly to our understanding of ethics: where I have quoted their actual words, it is because they have presented views or arguments more clearly or more forcefully than I could put them myself.

In his work The Cement of the Universe: A Study of Causation, Mackie makes an analysis of causality by prior philosophers and sets forth his theory of causality based on counterfactual conditionals.​ He argued that a cause is an "INUS condition" (insufficient but non-redundant parts of a condition which is itself unnecessary but sufficient for the occurrence of the effect).

[15] In metaethics, he took a position called moral scepticism, arguing against the objective existence of right and wrong as intrinsically normative entities on fundamental grounds.

The Times called the book "a lucid discussion of moral theory which, although aimed at the general reader, has attracted a good deal of professional attention.

[20] The philosopher Mary Midgley responded in 1979 with "Gene-Juggling", an article arguing that The Selfish Gene was about psychological egoism rather than evolution.