The oldest of four children, Simpson was born in 1913 in Beijing, China, to Daniel Ammen de Menocal, a banker from an aristocratic Cuban family, and Beatrice (Crosby) de Menocal, a New York City socialite.[1][2] The family lived in South America before settling in Boston, Massachusetts.[1][2]
Simpson married William Simpson in 1935 and moved to Locust Valley, New York;[3][4] they divorced seven years later.[1] In 1944, two years after moving to Manhattan, Simpson obtained (through a friend) a position at Harper's Bazaar, working in a photographer's studio.[1][2] She was then hired to work for the magazine itself, under editor Carmel Snow.[1]
In 1947, she left Harper's Bazaar to work at Vogue, where she would remain until 1972.[1] As a fashion editor, Simpson covered fashion shows and produced photo shoots.[2] She collaborated with the photographer Irving Penn on many of his iconic images.[4] She styled what would become Marilyn Monroe's final photo shoot, photographed by Bert Stern a month before her death.[4][5]
After leaving Vogue, Simpson worked at House & Garden magazine from 1972 until it was shuttered in 1993.[1]
In 2006, at the age of 93, Simpson became the oldest person to be featured in Vogue, when she appeared in its annual Age Issue.[6][2] In 2012, at age 99, she was featured in In Vogue: The Editor's Eye, an HBO documentary about the fashion editors at Vogue.[5][6][7]
Simpson was in a 35-year relationship with art dealer Paul Magriel; they lived in separate apartments in the same Manhattan apartment building throughout their relationship and did not marry.[2][4] Simpson owned a Paul Lester Weiner-designed modernist home in Amagansett, New York, built for her in 1963.[4][8] She spent her later years in a retirement community in Rye, New York.[1][2] She died on January 7, 2019, at the age of 105, in Rye.[1]