First, the teaser trailer from Focus Features:

Uploaded December 14, 2018

Then the official trailer:

Uploaded May 21, 2019

With more revelations in the UK trailer:

Uploaded by Universal Pictures UK, May 21, 2019

Downton Abbey: The Movie!
Coming our way September 2019!
We won’t have to wait much longer.

Director: Michael Engler
Writer: Julian Fellowes
Producers: Gareth Neame, Liz Trubridge, Julian Fellowes
Cast: Hugh Bonneville, Laura Carmichael, Jim Carter, Brendan Coyle, Michelle Dockery, Kevin Doyle, Joanne Froggatt, Matthew Goode, Harry Hadden-Paton, David Haig, Geraldine James, Robert James-Collier, Simon Jones, Allen Leech, Phyllis Logan, Elizabeth McGovern, Sophie McShera, Tuppence Middleton, Stephen Campbell Moore, Lesley Nicol, Kate Phillips, Maggie Smith, Imelda Staunton, Penelope Wilton