The National Museum of African American History and Culture announced Tuesday that Winfrey's gift, combined with her previous donation of $1 million, is its largest to date.
"I am so proud of African-American history and its contributions to our nation as a whole," Winfrey said in a statement released by the museum. "By investing in this museum, I want to help ensure that we both honor and preserve our culture and history, so that the stories of who we are will live on for generations to come."
Construction of the museum, which carries a $500-million price tag, started early last year on 5 acres at Washington's National Mall with a completion date set for sometime in 2015. The U.S. government is providing half of the funding for the museum, which will be the 19th addition to the Smithsonian, with the remainder to be raised by the museum.
Highlights will include more than 22,000 objects from African American history that span slavery through the civil rights area and into the 21st century. The museum will have a 350-seat theater for visiting performers, scholars, authors and filmmakers that carries the moniker of the media mogul.
Museum director Lonnie Bunch said in a statement: "Programming at the Oprah Winfrey Theater will mirror the museum's commitment to use African-American history and culture as a lens to see what it means to be an American and to help all Americans remember."
Bunch told the Associated Press that he's in talks with Winfrey, who also serves on the museum's 22-member advisory council, to add items from her career, including the microphone used by the former talk-show host.