Rooney, 21, from Croydon, is in the form of his life. Unbeaten this year he stormed to victory in July's Olympic trials to claim his first senior title.
He had to return embarrassed from the 2004 World Junior Championships because he didn't have a British passport. His parents are Irish.
But he will run for Britain the opening heats of the 400m on 18 August, with the final three days later, at 2055 BST, and the 4x400m relay on 23 August.
Rooney says if Olympic champ Jeremy Wariner is put "under pressure in the last 20m and he is not 100%, then you have a chance".
The BBC is not responsible for the content of external internet sites