The movie actor announced that Cyberpunk 2077 is set to go on sale on 16 April 2020.
The future-set role-playing game is being developed by CD Projekt Red, the studio behind the Witcher series.
Reeves - who has starred in the Matrix trilogy amongst other sci-fi movies - will appear in the title.
His brief appearance at the Xbox event drew huge applause with one attendee shouting: "You're breathtaking."
"No, you're breathtaking," the actor ad-libbed in reply.
Reeves' involvement guarantees positive publicity for Poland's CD Projekt, which had faced criticism for reportedly putting its team under pressure to do "extensive overtime" to have Cyberpunk 2077 ready to demo at E3.