>>10183Reincarnation was an integral part of the Greek Orphic mystery schools (see Plato's Phaedo, wherein he already calls this belief "an ancient doctrine"), and Gnostic Christianity is of course full of it, so the latest point at which this must've entered esoteric Jewish thought would've been in the heydays of Alexandria, some 2,300 years ago.
It became more widespread at the end of the middle ages with the works of Isaac Luria and the Galya Raza, see
https://pluto.huji.ac.il/~mselio/transmigration-46.pdf (israeli server!)
I have no idea how popular the belief was in the centuries in-between.
Did they believe in reincarnation before contact with the Greeks?
Maybe, I don't really know.
I do remember coming across one passage in the bible that spoke of "cycles" or something that did make me feel like it could hardly have been talking about anything other than reincarnation, but I can't find it right now.
Chabad of course claim that this was always part of Judaism, and that the Indians were in fact taught about reincarnation by a relative of Abraham.