determinist n.

1846, introduced by William Hamilton for "doctrine of the necessitarian philosophers" (who hold that human action is not free but necessarily determined by motives, regarded as external forces acting on the will or character of the person). See determine + -ism.

Determinism does not imply materialism, atheism, or a denial of moral responsibility; while it is in direct opposition to fatalism and to the doctrine of the freedom of the will. [Century Dictionary]

 From 1876 in general sense of "doctrine that everything happens is determined by a necessary chain of causation," from French déterminisme, from German Determinismus, perhaps a back-formation from Praedeterminismus.

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.