The Marvel film's director Marc Webb confirmed DeHaan's much-rumoured casting as Peter Parker's best friend in a Twitter message on Monday (December 3).
"Meet Harry Osborn. So excited to have him on board," Webb wrote.
Harry Osborn, who is the son of Spider-Man foe Norman 'Green Goblin' Osborn, was originally played by James Franco in director Sam Raimi's trilogy.
The character has a long and complicated history with Peter Parker in the comics, having first appeared in 1965.
He ultimately donned the Green Goblin costume following the death of his father Norman, although it is unclear how Harry will be portrayed in Webb's Amazing Spider-Man sequel.
DeHaan is best known for his roles in the hit HBO series In Treatment as well as the films Chronicle and Lawless.
The actor joins the returning Andrew Garfield and Emma Stone as well as Shailene Woodley, who will play Peter Parker's great love Mary Jane Watson.
Jamie Foxx has also been linked to the role of the villainous Electro.
The Amazing Spider-Man helmer Webb recently revealed that the next film will delve deeper into the disappearance of Peter Parker's parents.
Sony has announced that the sequel will be released in May 2014.
Watch a trailer for The Amazing Spider-Man below: