In 2023, he returned to Broadway to critical acclaim in the lead role of Rabbi Josef Roman Cycowski in Barry Manilow and Bruce Sussman’s Harmony.
[4] Zien's first major role was in 1977 at the Manhattan Theater Club in the musical The Redemption Center (by Ron Cowen, Seth Glassman, and Sandy Naishtat), opposite Alice Playten as the young couple.
[8] In 1998 Zien was featured in another Finn musical when he played a children's show host called Mr. Bungee, dressed as a frog, in A New Brain Off-Broadway at the Lincoln Center Mitzi E. Newhouse Theater.
[10] He appeared in the Off-Broadway play Isn't It Romantic by Wendy Wasserstein in a Playwrights Horizons production at the Lucille Lortel Theatre, opening in June 1984.
[12] Zien starred on Broadway in Ride the Winds (as Inari) (1974), The Suicide (as Victor Victorovich) (1980), Grand Hotel (as Otto Kringelein) (1989) and The Boys from Syracuse (as Dromio of Ephesus) (2002).
From April 1 to June 19, 2011, Zien appeared in the Roundabout Theatre Company's production of The People in the Picture, which played at Studio 54 on Broadway.
[17] Zien originated the role of Older Rabbi Josef Roman Cycowski of the famous Comedian Harmonists both Off-Broadway and on Broadway in the musical Harmony at both the Museum of Jewish Heritage at the National Theater Folksbiene (where he was nominated for a Drama Desk Award) and the Ethel Barrymore Theatre in 2022 and 2023, respectively.
In 1981, he appeared on Ryan's Hope as Daniel Thorne, the producer of the fictional Proud and the Passionate soap opera on the series in which the character Barbara Wilde (Judith Barcroft) was starring.
Immediately after Love, Sidney's cancellation, Zien was cast in a similar role on the ABC sitcom Reggie, an American adaptation of the British series The Fall and Rise of Reginald Perrin.
[19] In the 1990s, Zien was part of the ensemble cast of the CBS sitcom Almost Perfect (1995–96), playing neurotic screenwriter Gary Karp.