Enrolled as a member of an organization, and having a card to prove it; used especially to signify loyal dedication to that organization or the cause it supports
emphasis If you describe someone as, for example, a card-carrying feminist, you are emphasizing the fact that they believe strongly in and try to carry out the ideas of feminism
A card-carrying member of a particular group or political party is an official member of that group or party, rather than someone who supports it. I've been a card-carrying member of the Labour party for five years