The Chile Under-23 striker has joined the Red Devils for an undisclosed fee after they exercised an option to sign the 18-year-old that has been in place since 2009.
Red Devils boss Sir Alex Ferguson told the club's official website: "Angelo has made a tremendous impact on the game in his short career so far. "His pace is a great asset and he reads the game really well for someone of such a young age.
"We have a proud record of developing young talent and Angelo fits the profile of a United player - skilful, attacking and someone who plays the game with real flair."
Henriquez said: "I am thrilled to be joining the biggest club in the world. Manchester United is a great team and has a great manager.
"To be able to be part of that is a huge honour and I can't wait to get started. I hope I can be part of many successful years with United."
Source: team talk
Source: team talk