Sacheen Cruz Littlefeather was born Marie Louise Cruz on November 14, 1946, in Salinas, California. Her mother was a leather Stamper from Phoenix, Arizona, of French, German, and Dutch descent. Her father, an alcoholic who beat her mother, was from the White Mountain Apache and Yaqui tribes. The couple moved to California while her mother was pregnant. She was primarily raised by her maternal grandparents, Marie and Barney, and was Catholic as a child. Sometimes she lived with her mother; she recalls a trip through Mississippi when she was told to use the "black" water fountains and a sign that read, "No Dogs or Indians Allowed".

Littlefeather got in contact with actor Marlon Brando through her neighbor, Director Francis Ford Coppola. She wrote Brando a letter, asking about his interest in Native American issues, and he called the radio where she worked a year later. Brando had worked as an Activist with the American Indian Movement (AIM) since the 1960s and into the 1970s. In Washington, D.C., where Littlefeather was presenting to the Federal Communications Commission about minorities, they met and found in Common their involvement with AIM.

While she attended California State University, East Bay, she continued to look into her Native American identity. In Oakland, she worked with the Intertribal Friendship House. In 1969, she became a member of Indians of All Tribes and participated in the occupation of Alcatraz, when she adopted the name Sacheen Littlefeather. She learned more about Native American customs from elders and other protesters.

On a full scholarship to the American Conservatory Theater, she began acting education. Aspiring to become an Actress, Littlefeather picked up several radio and television commercial credits and joined the Screen Actors Guild. In 1970, she was named Miss Vampire USA, a promotion for Dark Shadows.

Playboy magazine planned a spread called "10 Little Indians" in 1972, and one of the Models was Littlefeather, but Playboy editors cancelled its publication due to the Wounded Knee incident. A year later in October 1973, after her Academy Award appearance fame, they ran the photographs of Littlefeather as a stand-alone feature. Littlefeather was personally criticized for what was seen as exploitation of her fame. Looking back at the photo shoot, Littlefeather later said, "I was young and dumb."

In 1972, Brando played Vito Corleone in The Godfather, which is considered one of the greatest films of all time. For the performance, he was nominated for Best Actor for the role at the 45th Academy Awards, which were presented on March 27, 1973, at the Dorothy Chandler Pavilion in Los Angeles, California. But before the ceremony, Brando decided that – as the favorite to win – he would boycott as a protest against the ongoing siege at Wounded Knee led by AIM and his views on how Native Americans were represented in American films. He called Littlefeather and asked her to appear on his behalf. "I was a spokesperson, so to speak, for the stereotype of Native Americans in film and television," she later said.

In 1979, she co-founded the National American Indian Performing Arts Registry, which later helped several actors join the production of Dances with Wolves. She shared an Emmy Award as an advisor to PBS's Dance in America: Song for Dead Warriors (1984). She also worked on the PBS shows Remember Me Forever and The Americas Before Columbus (both 1992), and she has produced films on Native American health. In 2009, she gave testimony in the documentary Reel Injun about Native Americans in film.

She continued doing activism and became a respected member of California's Native American community. In the 1980s, she led prayer circles for Kateri Tekakwitha, the first Native American Catholic saint. In 1988, she worked with Mother Teresa helping AIDS patients in hospice care, later founding the American Indian AIDS Institute of San Francisco. She campaigned against obesity, alcoholism, and diabetes, and specifically assisted Native Americans with AIDS, including her brother.

The speech was credited with bringing attention back to the Wounded Knee standoff, on which a media blackout had been imposed. Coretta Scott King called Littlefeather to thank her for the speech. In 2014, the 87th ceremony of the Academy Awards drew criticism for lack of diversity in nominations; Actress Jada Pinkett Smith, who boycotted the ceremony, cited Littlefeather as inspiration to do so.

In March 2018, a spokesperson announced that Littlefeather had developed stage 4 breast cancer. As of April 2018, Littlefeather resides in Northern California.