The 28-year-old also got the part to play the mythological Greek demi-god thanks to his impressive physique, said The Hollywood Reporter.
"It takes more than a good physique to portray the most legendary, mythological personality in history -- and Kellan has exactly that, personality. He's not afraid to explore the strengths and vulnerabilities of the character, and he impressed me with his passion and heart," Harlin said
The USD 70 million movie is expected to centre around a love story involving Hercules and the mortal Princess of Crete, who was promised to the titular character's older brother despite her love for him.
But Kellan isn't the only star set to take on the role of Zeus' son. Dwayne Johnson has signed up to portray the Greek demigod in 'Hercules: The Thracian Wars', which is expected to be released in July 2014.
Brett Ratner is directing the film, which is also set to star Rufus Sewell as Autolycus, the son of Olympian god Hermes.