Fenwick was born in Trinidad in 1907, the older sister of Violet Ethelred Krauth (who became actress Marian Marsh)[2] and Anthony Edward Krauth (who also acted, under the name "Tony Marsh").

In 1925, Harriet was one of the first 18 students chosen to open the Paramount Pictures School in New York City, along with Thelma Todd.

[3] The family moved again, to Los Angeles, California, when Harriet was a teenager starting in films.

[5] Films in which Fenwick appeared included Cross Country Cruise (1933, with Lew Ayres),[6] Mary of Scotland (1936, directed by John Ford and starring Katharine Hepburn),[7] Conquest (1937, with Greta Garbo), Arrest Bulldog Drummond (1939), Divorce (1945), and Street Corner (1948).

Later in her career, she appeared in television productions, including episodes of Gunsmoke (1957), and One Step Beyond (1960) Fenwick died in Woodland Hills, California in 1998, aged 91 years.