In the early twentieth century, psychology as discipline crystallised much of its epistemology and methods around positivism and the associated experimental method. This chapter explores the generally unthought-of, yet lasting contributions that the statesman and philosopher of holism, Jan Christiaan Smuts, has made to Anglo-American psychology. Whilst there are those in psychology who remain ambivalent towards holism, preferring knowledge claims based on elemental reductionism, the active adoption of holism via Smuts nevertheless transpired within certain threads of psychology and psychiatry. Jan Smuts lived an illustrious, prominent, and interdisciplinary life combining an erudite knowledge of biology and botany with contrasting and overlapping interests in philosophy, psychology, law, literature, and politics. As an important early theorist on holism, what impact did Smuts's philosophy have on personality theory within psychology? Smuts considered the thesis of holism as an apt refutation of the predominant reductionist psychology of his day; he was philosophically opposed to positivism.