Hammerstein was the son of interior designer Dorothy Hammerstein (née Blanchard) and lyricist Oscar Hammerstein II. He had four half-siblings, two through each of his parents' earlier marriages: William and Alice Hammerstein from his father's side, and Henry Jacobson and Susan Blanchard from his mother's side.
For many years he directed staged readings of notable playwrights, such as Jeff Wanshel, Ron Cowen, and Werner Liepolt as "American Triptych," under the auspices of George White and Lloyd Richards' National Playwrights Conference at the Eugene O'Neill Theater Center in Waterford, Conn.
Hammerstein was nominated for the 1997 Drama Desk Award for Outstanding Musical Revue for I Love You, You're Perfect, Now Change (as producer)[8] and the 1990 Drama Desk Award for Outstanding Director of a Musical for The Sound of Music.
Hammerstein had one child (Oscar Andrew) with his first wife Basia, two children (Will and Jennifer) with his second wife Millette Alexander, and one child (Simon) with his third wife Geraldine Sherman.[9][10] He died in Manhattan after suffering a heart attack.[9]