She was born in Chicago in 1898, the daughter of Ginevra and Charles Garfield King. (She, as with her mother and grandmother, was named after Leonardo da Vinci's painting Ginevra de' Benci.) Charles G. King was a wealthy Chicago businessman and financier. She was the eldest of three sisters and grew up amidst the Chicago social scene, even being a member of the elite "Big Four" Chicago debutantes during World War I. She attended the Westover School in Middlebury, Connecticut.
Ginevra first met Fitzgerald on January 4, 1915, while visiting her roommate from Westover, Marie Hershey, in St. Paul, Minnesota. They met at a sledding party and, according to letters and diary entries, they both became infatuated. They sent letters back and forth for months, and their passionate romance continued until January 1917. In August 1916, Fitzgerald first wrote down the words, thought to have been said to him by Charles King, that would later recur in the movie adaption of The Great Gatsby: "Poor boys shouldn't think of marrying rich girls."
On July 15, 1918, King wrote to Fitzgerald, telling of her engagement to William Mitchell, the son of her father's business associate. They married later that year and had three children. Then in 1937, she left Mitchell for businessman John T. Pirie, Jr. (of the Chicago department store Carson Pirie Scott & Company). That year she also met Fitzgerald for the last time in Hollywood; when she asked which character was based on her in The Beautiful and Damned, Fitzgerald replied, "Which bitch do you think you are?"
King later founded the Ladies Guild of the American Cancer Society. She died in 1980 at the age of 82.