Krantz was born Judith Tarcher on January 9, 1928 in New York City, the eldest child of an advertising executive and an attorney. After growing up in New York City where she graduated from the Birch Wathen School at age 16, she enrolled at Wellesley College, graduating in 1948.
After graduating, Krantz moved to Paris, where she worked as a fashion publicist. The following year, she returned to New York, where she embarked on a career in magazine journalism. She worked at Good Housekeeping before being promoted to Fashion Editor.
In 1953, Krantz attended a Fourth of July party hosted by her high school friend Barbara Walters. There she met her future husband, film and television producer and writer Stephen Falk Krantz. They were married for 53 years,