The 22-year-old from Shanghai will replace Antonio Giovinazzi at the Sauber-run team and race alongside the experienced Valtteri Bottas, who will join from Mercedes-AMG.
Zhou currently lies second in the standings in his third season of Formula 2 and, in a dual-campaign year, has won the Formula 3 Asia championship.
Alfa Romeo team principal Frédéric Vasseur said: “It’s a pleasure to welcome Guanyu Zhou to Alfa Romeo Racing. He’s a very talented driver, as his results in F2 have shown, and we’re looking forward to helping his talent flourish even more in F1.
“We’re also looking forward to welcoming all the new Chinese fans who will join the team: Alfa Romeo Racing is a historical brand and one that embodies the spirit of F1, and we will do our utmost to make the experience of our sport a great one in China.”
This likely shows that Alfa Romeo is looking to grow its road car brand in China, which is the world’s largest market for new cars.
Zhou said: “I dreamt from a young age of climbing as high as I can in a sport that I’m passionate about, and now the dream has come true.
“It’s a privilege for me to start my F1 racing career with an iconic team, a team that has introduced so much young talent into F1 in the past.
“To be the first ever Chinese driver in F1 is a breakthrough for Chinese motorsport history. I know a lot of hopes will be resting on me and, as ever, I will take this as motivation to become better and achieve more.”
Giovinazzi will depart Alfa Romeo at the end of 2021 after 62 grands prix, leaving F1 without an Italian driver, despite the presence of Alfa Romeo, AlphaTauri and Ferrari.
Alfa Romeo CEO Jean-Philippe Imparato said: “Alfa Romeo is extremely grateful to Antonio Giovinazzi for his strong contribution to the team over the years, not just from a sporting point of view. Antonio has embodied the Italian spirit of the brand, being an authentic ambassador every day.”