The pre-World War I show about a members of a wealthy family and those who serve them at their country mansion was a ratings hit when it aired in the United Kingdom and United States.
A second season is airing on British television now and is to premiere in America early next year.
"The show's impact has been greater than anyone could have ever imagined. When 'Downton' was originally conceived, it was mapped out across three series," producer Gareth Neame told The Hollywood Reporter. "But with ratings continuing to reach 11.4 million viewers, our expectations have obviously changed and there is no reason why the show won't run and run, as long as there is still an audience for it."