The actors will share voice-over duties for the feature-length film on the Sept. 11, 2001, terror attacks, directed by former NBC News producer Linda Ellman.
"I was in lower Manhattan that horrible day" when the World Trade Center collapsed, Swank said in a statement Friday. "I was drawn to the project by the amazing stories of the 9/11 families and survivors featured in the film, and I am proud that by contributing my voice to the project, I can help their voices to be heard."
"On Native Soil" will tell five stories of survival and examine the 9/11 Commission's final recommendations. The film features interviews with people such as the victims' families, Sen. John McCain (search), a former FBI counterterrorism official and the former head of the CIA's Osama bin-Laden (search) desk.
"I saw this film in a rough cut and wanted to become involved," said Costner. "It's honest, it's serious and it's not political. This film tells stories every American will and should want to know."