The Australian star, 33, said "There's no way to feel sad when you know you're this blessed" after she failed to receive a nod for best actress, but defended Gerwig who was excluded from the best director category.
"Obviously, I think Greta should be nominated as a director," she said, during a Sag-AFTRA panel discussion.
Ryan Gosling, left, and Margot Robbie, centre, with director Greta Gerwig on the set of Barbie. (AP PHOTO)
"What she did is a once-in-a-career, once-in-a-lifetime thing. What she pulled off, it really is. But it's been an incredible year for all the films.
"We set out to do something that would shift culture, affect culture, just make some sort of impact, and it's already done that and some, way more than we ever dreamed it would.
"That is truly the biggest reward that could come out of all of this
Robbie said she was "beyond ecstatic" that box office juggernaut Barbie landed eight Oscar nominations, including best supporting actress for America Ferrera, who plays Gloria, and best supporting actor for Ryan Gosling, who plays Ken.
Gerwig missed out as best director, but was named alongside her husband Noah Baumbach for best adapted screenplay, while Robbie lost out on a best actress nomination but was recognised for best picture as a producer.
Gosling spoke about his disappointment for Gerwig and Robbie after being snubbed in their individual categories.
"There is no Ken without Barbie, and there is no Barbie movie without Greta Gerwig and Margot Robbie, the two people most responsible for this history-making, globally celebrated film," he said.
"No recognition would be possible for anyone on the film without their talent, grit and genius."
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