Confirmation of the engagement ends months of speculation about the couple, both of whom are 38 and were reared in Australia.
They met in January 2005 at an awards dinner honoring them. It was hosted by the Australian government and held in Los Angeles, Urban's spokesman Paul Freundlich said.
Freundlich said he had no further details about the couple's engagement or their wedding plans.
A spokeswoman for the actress added only, "I'll leave that confirmation to Paul. That's the old-fashioned, traditional way of announcing such things."
People magazine reported earlier that Kidman had revealed her engagement to the publication in an interview Monday while discussing a weekend gala event she hosted in New York, accompanied by Urban.
"He's actually my fiance," Kidman, an Academy Award winner for her role in the 2002 film "The Hours," was quoted as saying. "I wouldn't be bringing my boyfriend."
People said Kidman was photographed in November wearing a ring on her wedding finger while walking arm-in-arm with Urban in Boston, Massachusetts.
Kidman, a goodwill ambassador for the U.N. Development Fund for Women, ended her 10-year marriage to Cruise in 2001. The couple have two adopted children.
Cruise's fiance, actress Katie Holmes, recently gave birth to their first child together, a daughter named Suri.
Kidman was born in Hawaii but brought up in Australia. Urban, a singer and guitarist, was born in New Zealand and grew up in Australia. He won a Grammy in 2005 for best male country vocal performance for the song "You'll Think of Me."
