Fawcett died of cancer in 2009 at the age of 62. She and O'Neal had been together off and on for more than 20 years.
Her nephew, Greg Walls, and O'Neal donated objects from the private collection of her estate to the museum during a ceremony Wednesday.
Among the items bestowed upon the museum are the red swimsuit from her iconic 1976 poster, an original copy of the swimsuit poster, her personal "Charlie's Angels" script book, a Farrah Fawcett swimsuit jigsaw puzzle, an original 1977 Farrah Fawcett doll and a Farrah's Glamour Center hairstyling head.
The objects will be a part of the museum's Division of Culture and the Arts and will go on display this summer, the Smithsonian said.
"Farrah Fawcett has made an enduring impression on American popular culture," Brent D. Glass, director of the museum, said in a statement. "We are pleased to welcome this donation into our entertainment collections."
"It's an honor to see Farrah's famous red bathing suit donated to the Smithsonian Institution, celebrating her place in pop culture," O'Neal added. "The swimsuit is exactly where it belongs, and I know Farrah is looking down on us today flashing that big smile that we all loved."