In a press conference to promote The Hobbit: An Unexpected Journey, Director Peter Jackson discussed the casting Martin Freeman as Bilbo Baggins and defended the decision to expand The Hobbit into another trilogy.

"Martin was the only person that we wanted for that role, and that was really before we met Martin. We knew him from The Office and Hitchhiker’s Guide [to the Galaxy], and we just felt he had qualities that would be perfect for Bilbo. The stuffy repressed English quality. He’s a dramatic actor, he’s not a comedian, but he has a talent for comedy."

Because Martin was contracted to BBC's Sherlock, "We were in trouble. I was really panicking. I was having sleepless nights. We were probably six weeks away from the beginning of the shoot, and we hadn’t settled on anyone else, and I was torturing myself by watching Sherlock on an iPad at 4 o’clock in the morning."
Read more »

Peter Jackson On Casting Martin Freeman, Trilogy Choice. There are any Peter Jackson On Casting Martin Freeman, Trilogy Choice in here.