The news has been expected for some weeks, with the Japanese driver having begun his preparations with an outing in a 2018 Toro Rosso at Imola last month.
He enjoyed his first run in the current car and on proper race tyres in Abu Dhabi on Tuesday, setting the seventh best time of the day.
The 20-year-old, who is a protege of both Red Bull and Honda, will be the first Japanese driver to complete at the top level since Kamui Kobayashi in 2014.
Tsunoda made a big impact in the FIA F3 series in 2019 with the unfancied Jenzer team, winning the sprint race at Monza.
He was fast-tracked into the Carlin F2 team for this year and was a regular points scorer from the off. He won feature races at Spa and Sakhir, and a sprint race at Silverstone, and after strong end to the season he finished third in the championship.
Tsnuoda is highly regarded by Red Bull boss Helmut Marko, who told Motorsport.com in Abu Dhabi: “I love him! His speed, the way he overtakes, but also how quickly he learns how to nurse the tyres, and all of that.”
AlphaTauri boss Franz Tost said that Tsunoda has already impressed the Faenza outfit.
“Red Bull has been following Yuki’s career for a while now and I am sure he will be a great asset to our team,” said the Austrian.
“Watching him in F2 this year, he has demonstrated the right mix of racing aggression and good technical understanding. During the test in Imola in November when he drove our 2018 car, his lap times were very consistent over a race simulation, he progressed throughout the day and gave our engineers useful feedback.
“In addition, his integration with the Honda engineers has been seamless, which certainly helps. At the test in Abu Dhabi this week, he proved to be a fast learner and that he is ready to make the step to F1.”
Tsunoda said: “Like most racing drivers, it has always been my goal to race in F1, so I am very happy with this news.
“I want to thank Scuderia AlphaTauri, Red Bull and Dr Marko for giving me this opportunity, and of course everyone from Honda, for all their support so far in my career, giving me great opportunities to race in Europe.
“I must also thank the teams that I have raced with to get to this point, particularly Carlin, with whom I have learned so much this year. I realise that I will be carrying the hopes of a lot of Japanese F1 fans next year and I will be doing my best for them too.”