1st Grandchild's Christening

I agree with Synonymous. Assuming both you and your partner have been invited, if your ExH says he's not going for any reason, then he needs to tell the parents and they need to make the next move. Stick to your guns and don't discuss it any further with him. This is about his pride.

If you keep a dignified silence and he turns up at the event, is he likely to cause trouble on the day?

Does your son or daughter (parent of the baby) have an opinion on all this?

Welcome millymolly
Congratulations on your first Grandchild.

I am sorry you are facing acrimony on what should be a very happy family occasion. What is the attitude of the baby's parents and what are the various states of relations between the various parties as that will clearly make a difference.
In any case the baby's grandfather cannot be allowed to spoil this occasion which is your DGD's very first formal event. He is not thinking at all as obviously there will be other events throughout her life so, to be consistent, he will never attend anything! This is not his event and it is not his prerogative to decide on a guest list either.
It is a fact, not generally understood, that services in a church are open to all.
I would not take part in any discussion at all since it is not up to you either. Do not grace his statements with any reply directly to him whatsoever. It sounds to me as if he is just baiting you and looking for an opportunity to cause trouble for which he can then blame; you and your OH. Don't get drawn in and keep a dignified silence both now and at the Christening. Just relax and enjoy the service and the occasion.

Have you decided what gift you will giving your little GD?

How long has your partner known your children?

It's his choice and by the sound of it nobody will miss him. Your partner is a far kinder man and I'm sure he would be missed if he wasn't there. Stick to your guns and if he changes his mind, so be it.

I think you should stick to your guns. If he chooses not to attend that's his choice. I do feel sorry for the parents of the little one being christened though. Its their big day. What are their views or do you not want to burden them with all this?