There were some conflicting reports on this topic, but it's finally been confirmed that Darth Vader will have a very important — albeit small — role in the film. You can see brief looks at him in the recently released trailers, and "He will be in the movie sparingly," Lucasfilm president Kathleen Kennedy told Entertainment Weekly. “But at a key, strategic moment, he’s going to loom large.” Kennedy also let slip that James Earl Jones, 85, will once again provide Vader's menacing voice, adding a sense of authenticity to the project.
The EW article additionally revealed that Rogue One is taking place around 19 years after Revenge of the Sith, which ended with Anakin Skywalker losing his limbs and nearly being burned to death after fighting Obi-Wan, leading to his choice to put on the life-saving black armor his character is known for. At this point, Vader has yet to rise to the level of infamy he has in A New Hope, but is instead functioning as more of the Emperor's brutal enforcer, someone who the Rebels aren't completely aware of.
“Vader doesn’t really play by the rules," Lucasfilm’s chief of story development, Kiri Hart, told the magazine. “He’s present in the military structure, but he’s not beholden to it. He’s not accountable to anybody, really, except Palpatine.” Whether or not this iconic villain will have any face-to-face action with the protagonists is still unconfirmed, though we do know that he will have some scenes with Director Krennic.
