The 22-year-old has put pen to paper on a deal until 2027 with the option of an additional year.
The Red Devils have been linked with the former Sao Paulo winger all season and they have finally gotten their man who played a vital role for Ajax under Erik Ten Hag last season.
He has expressed his delight at the opportunity to play for Manchester United.
"This is an incredible moment in my career to join one of the most iconic clubs in the world," said Antony.
"I'm thankful to everyone who has believed in me, especially my family and all my coaches and teammates, because I could not have gotten here without them.
"Playing under Erik ten Hag at Ajax was perfect for me and my development. His style of football and coaching brings out the best in me, and I am excited by what he has told me about his plans and ambitions in Manchester."
Antony scored 24 goals and registered 22 assists for Ajax in all competitions after he joined them from Sao Paulo in 2020.
He is expected to make his Premier League debut against Arsenal on Sunday at Old Trafford.