の一員だ

is a member of

→ の
phrase Uncommon #16,891
is a member of Used to say that someone belongs to or is part of a group, organization, team, or family.
JA: 私はこのチームの一員だ。
EN: I am a member of this team.

彼は野球部の一員だ。

He is a member of the baseball team.

彼女はバスケットボール部の一員だ。

She is a member of the basketball team.

君はいまやエリート集団の一員だ。

You're now part of an elite group.

調理場の一員だよ

I'm part of the kitchen staff.

— レミーのおいしいレストラン (2007)