Is rennet a halal ingredient?

So yes inshallah it's permissible but there are two views just to be aware of. The first view is that of the Hanafi Madhab and also a narration from Imam Ahmed where it's permissible because rennet comes from a part of an animal that is not living. So regardless of how that animal is slaughtered because it's not a living part it will be permissible and also they mention narrations about how some of the companions of the Prophet Muhammad had cheese from the Magians and from those of the Christian faith as well. So they mention that that therefore would be permissible. According to the other Madhabs it would not be permissible as they would see it as something which is najis. So there are two views just so that you are aware.