Co-nominee Jennifer Lawrence won the Golden Globe in this category on Jan 12. Both actresses are nominated again for best supporting actress for the Academy Awards.
This was the first award of the evening, and a joyous moment for the stunning young actress and admiring audience who were enchanted by probably the best acceptance speech of the awards show.
In "12 Years a Slave", Nyong'o plays the young slave girl Patsey who is brutally beaten by her master Edwin Epps (Michael Fassbender) for leaving the property to get a bar of soap and is also assaulted by his wife (Sarah Paulson) for arousing his attention.
In her acceptance speech, Nyong'o thanked Solomon Northrup who wrote his memoirs in "12 Years a Slave" for "a story hard to tell but well told" and director Steve McQueen "for taking a flashlight and shining a light on the floorboards of this nation and reminding us of what we stand upon".
Nyong'o also thanked her Alma Mater, Yale School of Drama and the crew of the film "for making Patsey's scars so real to me", and for helping her to find Patsey's "voice and heart".
The first person she said she called was her father after getting the part in "12 Years a Slave".
"Daddy do you know Brad Pitt? I'm going to be in a movie with him", she exclaimed. "I don't know him personally, replied her father, "but I'm glad you got a job!".
"So am I!", she told the SAG audience.
Born in Mexico City of Kenyan citizenship and educated in the US (Hampshire College, Yale), Nyong'o worked on production crews for films such as "The Constant Gardener" (Fernando Meirelles) and "Namesake" (Mira Nair), and was also featured in the short award winning film "East River" (2008) by Marc Grey. She also starred in the South African miniseries "Shuga" (2009-2012). This year she will appear in Jaume Collet-Serra's action thriller "Non Stop" starring Julianne Moore and Liam Neeson to be released on Feb 28..
At 29 she made the award winning documentary "In My Genes" (2008) about Kenya's albino population.
Next stop for Lupita Nyong'o is the BAFTA British Film Awards in London on Feb 16 where she is nominated for best rising star, followed by the Academy Awards hosted by Ellen Degeneres on March 2.