Carrie-Anne Moss will also return as Trinity, with Lana Wachowski coming back as director and co-writer after creating the franchise with her sister Lilly.
"Many of the ideas Lilly and I explored 20 years ago about our reality are even more relevant now," Wachowski said in a statement published by Variety.
"I'm very happy to have these characters back in my life and grateful for another chance to work with my brilliant friends."
Lana wrote the new film's script along with sci-fi novelists Aleksandar Hemon and David Mitchell.
Although Lilly is not involved in the next Matrix movie, she gave her blessing to it in an interview earlier this year.
"I like it when stories go out into the world and then come back to you in different ways," she told Slash Film.
"That's what storytelling is all about. I'm part of a bigger thing. I don't have any ownership over stuff like that, so whatever story anybody wants to tell, I can't wait to hear.
"I hope it’s better than the original."
A reboot of the Matrix franchise has been rumoured since 2017, when The Wire star Michael B Jordan was said to have a lead role.
Keanu's return to the role comes at a time when his career is enjoying somewhat of a renaissance and is sure to thrill fans.