Fairley, who won the 2010 Lombardi Award, received defensive MVP honors in Auburn's 22-19 BCS championship victory over Oregon.
"I was thinking, 'What more could I accomplish my senior year?'" Fairley said.
During his junior season with the Tigers, the Mobile native totaled 60 tackles, 11.5 quarterback sacks and a school-record 24 tackles for loss.
"Nick emerged into a very dominant player this season and was a key factor for the success of our championship run," Auburn head coach Gene Chizik said. "His ability to control the line of scrimmage was truly amazing. We know that Nick loves Auburn, but this decision is in the best interest of him and his family. We wish him well as he takes the next step in his football career and life."
Following the national championship game, Fairley consulted many people to help make his decision.
After talking with his parents in Mobile, Fairley said he went on a long ride by himself to decide what was best for him and his family.
This was Fairley's second season at Auburn, after transferring from a junior college.
"It's crazy for me to be in this position," Fairley said. "Coming into this year, I didn't think things were going to be this big. I didn't know I was going to have a big year like that."