party member
Refers to a member of a political party or similar organization. Neutral term.
彼は自民党の党員です。
He is a member of the Liberal Democratic Party.
党員証を提示してください。
Please show your party membership card.
He became a member of that party last month.
She took part in the election campaign as a party member.
In recent years, the number of party members has been decreasing.