Hemingway was born in Mill Valley, California, the third daughter of Byra Louise (née Whittlesey) Hemingway and Jack Hemingway, a writer. Joan Hemingway is her sister. Another sister, Margaux Hemingway, was an actress and model who died of a barbiturate overdose at age 42 in 1996.

She was featured in Superman IV: The Quest for Peace (1987) as Lacy Warfield. Subsequently, released additional footage showed an expansion of her role. She also co-starred in the 1991–93 ABC series Civil Wars. She was cast as the female lead in Darren Star’s CBS drama Central Park West for the 1995–96 season; however, the show fared poorly with both critics and viewers, and after 13 episodes Hemingway was told that the show wanted her to accept a huge pay cut and demotion to recurring character status. She quit the series, which only lasted eight more episodes before being cancelled. In 1996, she had a leading role in the British TV movie September, playing the wife of Michael York.

Hemingway married Stephen Crisman. Together, they had two daughters, Dree Hemingway and Langley Fox. They separated in 2008 and divorced the following year.

Hemingway worked on the documentary film Running from Crazy, directed by Barbara Kopple and produced by the Oprah Winfrey Network chronicling the Hemingway family’s history of suicide, substance abuse and mental illness, shown at the Sundance Film Festival in 2013. In October 2013, Hemingway received a humanitarian award from the San Diego Film Festival for her role in the documentary.

In a 2013 television documentary film, Running from Crazy, Hemingway, then 51, talked of her bouts of mental illness and her still lingering issues with her siblings. She spoke of her family’s struggles with alcoholism, mental illnesses and suicide. (In particular she mentioned how her sister Margaux’s suicide continued to haunt her.) She also made claims that her parents’ marriage was abusive and unhappy, and about abusive incidents in her childhood.

As of early 2011, Hemingway was romantically linked with former stuntman Bobby Williams, with whom she has co-authored a self-help book. In April 2015, Williams was described as Hemingway’s partner. She practices Transcendental Meditation.