I incline to distinguish historicism from determinism. In my view neither implies the other.
As a historicist, I argued that human
life was ineluctably historical, so explanations of ideas, texts, actions, and
practices should rely on historical narratives, not appeals to formal classifications, correlations, systems, or models. (Mark Bevir, 'Post-Analytic Historicism', Journal of the History of Ideas, Vol. 73, No. 4 (October 2012), pp. 657-665: 657.)
... I defended a radical historicism, according to which
human life consists solely of a flux of activity without any basis in a formal
structure or teleological movement. There are just particular individuals
engaged in particular actions in accord with their particular beliefs and
desires. My radical historicism restated the idea that explanations of human
life should take the form of historical narratives. (Bevir: 658.)
As I understand this, the central historicist claim is that human societies are historically specific. A society is to be studied and known as a unique configuration of institutions and practices employing concepts, traditions, and self-images (a list, not a complete enumeration) that are special and exclusive to itself. This is not a conservative perspective since there is no assumption or implication that a society is unchanging. Nor does it deny that a society shares no institutions and practices with any other society; overlap is possible and actual but a core of uniqueness remains.
Even so, overlaps will be subject to qualification. Both the United States and the Fifth French Republic are presidential regimes and share a common political taxonomy to that extent; but it would be crude to suppose that we can properly disregard the nuances that differentiate them. A historicist approach is sensitive to the nuances and is more attentive to differences than to similarities. A thoroughgoing historicist might go so far as to say that it is only the nuanced differences that are real; taxonomies are mere devices of convenience enabling superficial generalisation. The US is a democracy, so is modern France, so was ancient Athens. Do we really gain insight into any of them by lumping them together under this category ?
Historicism also recognises that questions of incommensurability will arise. You can say that Aristotle's eudaimonia means *happiness** as long as you know that it doesn't. Nothing in current English or related languages precisely corresponds to the Aristotelian concept.
Suppose we take Classical Marxism as a form of determinism. There is some case for this if take Marx to be saying that a society's political and cultural phenomena belong to a superstructure which is ultimately explicable in terms of functionality to its economic base. The base causally explains why there is a superstructure, what its features are, and why and when they change.
(I'm aware that the question whether Marx was a strict determinist, despite his reference in Capital to 'the iron laws of history', is a tricky one. I can't go into it here for reasons of space.)
There seems to be no logical connection between historicism and determinism at least to this extent - one might adopt the idea of historical specificity outlined above without accepting any form of social determinism. Historicism and determinism are not incompatible - logically inconsistent - but (it may be my blindside) I cannot see that either logically implies the other.