The news was announced Monday by Kidman's publicist, Catherine Olim. It was also posted on Urban's Web site.
"The couple are thrilled," Olim said.
Kidman and Urban are in Sydney, Australia, where the 40-year-old actress has been working on Baz Luhrmann's epic romance, "Australia."
She was due to start filming for Stephen Daldry's post-World War II drama, "The Reader," later this month, but her Australian publicist, Wendy Day, said she understands Kidman has withdrawn from the movie because of her pregnancy.
A call to the Weinstein Co., which is producing "The Reader," wasn't immediately returned.
Speculation had been increasing in recent weeks over Kidman's maternal condition.
"For years I've seen speculation and for years it's never been right, so I didn't think it was right this time," Day said. "And then she's just rung this morning."
Urban, a Grammy-winning singer and guitarist raised in Australia, and Kidman were married in June 2006.
Kidman has two children, Isabella, 14, and Connor, 12, from her marriage to Tom Cruise. They divorced in 2001.
She recently told Vanity Fair magazine she had a miscarriage early in her relationship with Cruise, leading them to adopt.
"I feel enormous love for whoever my children's birthparents are," Kidman told Ladies' Home Journal in 2006. "And if my children choose to go find them at some stage, I can't wait. Because - it's the weirdest thing - I actually feel (they're) very connected to us as a big, strange family, and whether they choose to search for them or not, who knows."
Cruise married Katie Holmes in November 2006, seven months after the birth of their daughter, Suri.
