Is Northern Ireland Part Of The Commonwealth?

Yes, because it’s part of the United Kingdom, a member state of the Commonwealth, the government of which is responsible for Northern Ireland’s external relations.....

It has its own team in the Commonwealth Games, as do all the other constituent countries, crown dependencies and overseas territories of the UK, and also participates in the Commonwealth Parliamentary Association.

However, during the years that the Northern Ireland Assembly was suspended, Northern Ireland was not directly represented in that forum, and was only readmitted by its General Assembly in 2007.

In the unlikely event that the United Kingdom ceased to be member of the Commonwealth, all of its constituent countries, including Northern Ireland, would cease to be parts of the Commonwealth.

Were Northern Ireland to become part of the Republic of Ireland, which is not a member of the Commonwealth, it would cease to be part of it, just as it would cease to be part of NATO, which the Republic is not a member of either.