According to The Hollywood Reporter, the Sons of Anarchy star will play the human lead in the Pan's Labyrinth director's highly-anticipated monster movie.
Del Toro was chosen to helm Pacific Rim in mid-March. He was previously attached to direct a big-screen adaptation of H.P. Lovecraft's At The Mountains of Madness until it was announced that the project had been placed on hold.
In Pacific Rim, Earth is invaded by powerful aliens that target the countries along the Pacific Ocean. In response, humanity decides to make giant robots in order to combat the extraterrestrials.
Hunnam plays Jackson 'Jax' Teller on the FX series Sons of Anarchy. He has also starred in Children of Men, opposite Clive Owen, and Cold Mountain.
The 31-year-old actor will reportedly portray a pilot of one of the robots created to fight the aliens.
Pacific Rim will begin filming this September with a scheduled Summer 2013 release.