The Rise of Skywalker, which will feature the late Carrie Fisher in her last screen role, will be released on 20 December.
Writer and director JJ Abrams unveiled the first teaser at a Star Wars celebration in Chicago.
Actors from the original trilogy making a return include Anthony Daniels, as C3PO and Billy Dee Williams, who last played Lando Calrissian in Return of the Jedi.
Daisy Ridley, Adam Driver, Oscar Isaac, John Boyega, Lupita Nyong’o and Domhnall Gleeson are among the stars of the new trilogy, which is set after the first three films, to return in the swansong.
Abrams told the audience of Star Wars fans in Chicago: “This movie, in addition to being the end of three trilogies, it also has to work as its own movie.
“It’s about this new generation and what they've inherited the light and the dark, and asking the question as they face the greatest evil, are they prepared? Are they ready?”
Abrams said unused footage shot during the making of The Force Awakens had been used to create the scenes with Fisher’s character Leia. She passed away before the previous film was released.
Abrams added: “You don't recast that part and you don't suddenly have her disappear.
“The weird miracle of having a number of scenes from Force Awakens that had got unused, looking at those scenes and starting to understand that there was an actually a way to use those scenes and continue her story, so that it would be her.
“The idea of having a CG character was off the table … we said, ‘what if we could write scenes about her so it’s her performance?’
“Every day it hits me that she's not here. It’s so surreal because we are working with her still, if that makes sense. She’s in scenes. She’s alive in scenes.”