Some in the audience booed her. John Wayne, who was backstage at the time, was reportedly furious. The 1973 Oscars were held during the American Indian Movement's two-month occupation of Wounded Knee in South Dakota.
In the years since, Littlefeather has said she's been mocked, discriminated against and personally attacked for her brief Academy Awards appearance.
In making the announcement, the Academy Museum shared a letter sent June 18 to Littlefeather by David Rubin, academy president, about the iconic Oscar moment. Rubin called Littlefeather's speech "a powerful statement that continues to remind us of the necessity of respect and the importance of human dignity".
"The abuse you endured because of this statement was unwarranted and unjustified," wrote Rubin. "The emotional burden you have lived through and the cost to your own career in our industry are irreparable. For too long the courage you showed has been unacknowledged. For this, we offer both our deepest apologies and our sincere admiration."
'We Indians are very patient - it's only been 50 years!'
Littlefeather, in a statement, said it is "profoundly heartening to see how much has changed since I did not accept the Academy Award 50 years ago".
"Regarding the Academy's apology to me, we Indians are very patient people - it's only been 50 years!
"We need to keep our sense of humour about this at all times. It's our method of survival."
At the Academy Museum event in Los Angeles, Littlefeather will sit for a conversation with producer Bird Runningwater, co-chair of the academy's Indigenous Alliance.
In a podcast earlier this year with Jacqueline Stewart, a film scholar and director of the Academy Museum, Littlefeather reflected on what compelled her to speak out in 1973.
"I felt that there should be Native people, black people, Asian people, Chicano people - I felt there should be an inclusion of everyone," she said. "A rainbow of people that should be involved in creating their own image."
