McCain described his plans to run before an Arizona Chamber of Commerce luncheon in Phoenix. He has signaled on several occasions in recent months that he was planning to seek a sixth term, but is now formally entering the race.

His appearance before a pro-business crowd comes ahead of a race in which he will likely face a challenge from the right amid tea party dissatisfaction over his record in the Senate. The Republican Party is currently divided between pro-business and conservative factions, and McCain's announcement location put him in friendly territory as he begins the race.

McCain will be 80 by Election Day, but says he is in great shape and has much work to do in the Senate.