The law is quite complicated in this respec
Delph - law is actually quite simple - anyone born to a Polish parent(s) is considered Polish citizen.
What he needs to do is the following:
- get his unabridged birth certificate (passport is not enough)
- register his birth certificate in USC (Polish authorities for registering births, marriages etc) - the procedure is called "Umniejscowienie Aktu Urodzenia" (additional documents may be required - like parents birth certificates, better to check)
- get Polish birth certificate and apply for Polish ID.
I recently enquired about the procedure as my son born in South Africa does not have Polish passport yet, and that's what I was told at the embassy.
my parents (both deceased now) had to give up their Polish passports
If your parents gave up their passport you might not have right to become Polish based on descendence.
But you can still live in Poland and apply for Polish citizenship after a while.