The Italian squad has the only seat available for the 2022 season, and Giovinazzi was still hopeful of securing another year at the Hinwil-based squad, admitting earlier this season that he was not looking elsewhere.
However, on Tuesday morning the team made the announcement that it will not retain Giovinazzi for next year.
“Saying goodbye to a driver is never easy, especially so in the case of Antonio, who has been part of the team for so long,” said team boss Fred Vasseur in a statement.
“As we part ways, we will cherish the memories of the good times and learn lessons from the bad ones, knowing these moments all made us grow together as a team.
“We wish Antonio the best for his future after the 2021 season: before then, we still have three races to achieve some good results together and finish the year strongly,” he added.
Giovinazzi, who joined Alfa in 2019, was the first Italian to compete in Formula 1 full time since the 2011 season.
The Italian racer has scored 19 points in his three seasons with Alfa Romeo, but only one this year compared to teammate Kimi Raikkonen’s 10.
Giovinazzi made his grand prix debut in 2017 when the team was known as Sauber, replacing Pascal Wehrlein in Australia and China after the German was injured in the Race of Champions.
The 27-year-old is to be replaced by Guanyu Zhou.
Zhou, who took part in Friday practice for the Austrian Grand Prix with Alpine this year, will become the first Chinese driver to compete in Formula 1.
Why Alfa Romeo chose Zhou for its F1 team
The 22-year-old from Shanghai will partner Valtteri Bottas at Alfa Romeo, the Finn leaving Mercedes at the end of a campaign after five seasons racing alongside Lewis Hamilton.
Zhou is currently second in the Formula 2 standings with the two rounds, and six races, in Saudi Arabia and Abu Dhabi remaining.