From Halopedia, the Halo wiki
The Halo film, officially confirmed in 2005, was a film project in development until its ultimate cancellation in 2006. The film, intended to be produced by Peter Jackson and Fran Walsh and directed by Neill Blomkamp was postponed indefinitely when funding studios 20th Century Fox and Universal Pictures pulled out due to monetary concerns.
The Halo film was to be filmed in live action with special effects, along with props and costumes, created by WETA Workshop and WETA Digital. WingNut Films, a New Zealand-based production company known for collaborating with Jackson on The Lord of the Rings trilogy, were also to be a part of the project.
When plans for the film eventually fell through, Jackson and Blomkamp instead started production on District 9. Many elements from the cancelled Halo film were re-used or adapted for District 9, including the basic Warthog and Pod infector designs.
Script, director and financial arrangement
Financial problems and cancellation
Halo 4: Forward Unto Dawn and Halo: Nightfall