Efron, who turned 21 last week, has reportedly agreed to a £6 million deal to appear alongside Johnny Depp in the fourth instalment of the popular Disney franchise.
The deal also ties him to a fourth High School Musical Movie, something he had said he would previously not do.
Efron has found international fame in the role of Troy, the school basketball star, but had said it was "time to grow up".
Thousands of screaming fans turned out to greet Efron when he arrived at the London premiere of High School Musical 3 along with co-star and girlfriend Vanessa Hudgens.
Efron is also expected to star in a remake of 80s favourite Footloose, which originally starred Kevin Bacon.
Depp, 45, currently filming Tim Burton's adaptation of Alice in Wonderland where he plays The Mad Hatter, will reportedly make £30 million reprising his role as Captain Jack Sparrow.
A source told The Sun: "Zac was extremely interested. But Disney realised they couldn't make the fourth Pirates movie without Johnny. They had to offer him a small fortune to do it."
Keira Knightley is expected to reprise her role as Elizabeth Swann although it is not thought Orlando Bloom will return.
It is rumoured the fourth Pirates film will focus on Jack Sparrow's quest for the Fountain of Youth.