Pitt's publicist, Cindy Guagenti, told The Associated Press on Wednesday that Jolie is pregnant and that Pitt is the father, confirming People magazine's earlier report.
"Yes, I'm pregnant," the magazine quoted Jolie as telling a charity aid worker Monday in the Dominican Republic, where she is filming "The Good Shepherd" with Matt Damon.
The news comes one month after papers were filed to make Pitt the adoptive father of Jolie's two children. Jolie sought to change the names of the children to Zahara Jolie-Pitt and Maddox Jolie-Pitt.
Pitt accompanied Jolie to Ethiopia in July to pick up Zahara, now 1. Jolie's adopted son, now 4, is from Cambodia.
Jolie's father, Jon Voight, was reached Wednesday morning for his reaction by entertainment TV show "Access Hollywood." The Oscar-winning star of 1978's "Coming Home" said he had not spoken to Jolie, but said, "Angie is my daughter and I am always wishing the best for her."
Previously, Jolie, 30, and Pitt, 42, had not publicly acknowledged their relationship despite increasingly frequent sightings of the couple. They had been spotted together across the globe: in Canadian shopping malls (near Pitt's movie set for "The Assassination of Jesse James by the Coward Robert Ford"), vacationing on African beaches and, most recently, in Pakistan.
In November, Pitt and Jolie, a goodwill ambassador for the U.N., toured quake-devastated areas in Pakistan. Jolie also met with Pakistani President Gen. Pervez Musharraf.
Jolie, whose films include "Lara Croft: Tomb Raider" and "Alexander," is divorced from actors Billy Bob Thornton and Jonny Lee Miller.
Pitt, the star of films including "Ocean's Eleven" and "Troy," had no children from his four-year marriage to Jennifer Aniston, which ended in divorce last October. The couple cited irreconcilable differences. Pitt has denied Jolie was behind the split.
Pitt and Jolie also starred together in "Mr. and Mrs. Smith" last year.