The star of "Minority Report," "In America" and "Sweet & Lowdown" is due in January and the father of the baby is her fiance, Harry Holm, the son of actor Ian Holm.
"It is wonderful news. They are both very excited and looking forward to having their new baby," Morton's publicist, Karon Maskill, told the Web site.
The 30-year-old actress has a 7-year-old daughter, Esme, from a previous relationship with British actor Charlie Creed-Miles.
Morton met her 26-year-old fiance in 2005 when he directed her in a video for the band, The Victims.
Holm proposed to Morton in Paris in May 2006 on her 29th birthday and the couple was expected to marry last fall, but deferred because of career demands.