Literally 'святой воин'.
But note that this combination of words is relatively rare thing in Russian because adjective 'святой' here is indistinguishable from noun 'святой (saint)' and saints have weak association with killings. It is preferred to say like 'saint who is known for his battle achievements' or something like that. Alexander Peresvet is called 'воин-монах (monk-warrior)' for example.
However it can be said so.