By Agence France-Presse
The final installment of the Skywalker saga -- which began in 1977 with "Episode IV: A New Hope" -- is due for release worldwide in December next year.
It picks up the saga after the protagonist, Hamill's Luke Skywalker, appeared to have been killed off in the last episode. Fisher's Princess Leia was still alive at the end of 2017's "The Last Jedi" but the actress herself died a year earlier, in December 2016.
"We desperately loved Carrie Fisher," said J.J. Abrams, who is back at the helm for "Episode IX," having directed "Episode VII: The Force Awakens" in 2015.
"Finding a truly satisfying conclusion to the Skywalker saga without her eluded us. We were never going to recast, or use a CG character," he added in a statement.
Disney said Fisher's role would be gleaned from previously unreleased footage from "The Force Awakens," with the blessing of her daughter, Billie Lourd.
It is not the first time Fisher's likeness has featured in a "Star Wars" movie despite being absent from its filming.
"Rogue One," a 2016 spin-off from the main series, directed by Gareth Edwards, had been in theaters for a couple of weeks when Fisher's death from a heart attack was announced.
A much younger version of Fisher as Leia appears in that movie, thanks to the controversial application of computer wizardry to animate her image.
Returning cast members for the final episode include Daisy Ridley, Adam Driver, John Boyega, Oscar Isaac, Lupita Nyong'o, Domhnall Gleeson, Kelly Marie Tran and Joonas Suotamo.
Naomi Ackie and Richard E. Grant are among the new faces, while old "Star Wars" hands Anthony Daniels and Billy Dee Williams return as C-3PO and Lando Calrissian.
Composer John Williams, who has scored every chapter in the "Star Wars" saga, continues his unbroken run for the next adventure.