Macey was born in Rochford, Essex. He started out in athletics as a high jumper, triple jumper and javelin thrower but graduated up through the octathlon to settle on the decathlon. He was also on the books of Arsenal as a youngster but gave up football to train for the World Junior Championships in 1995. Macey's major breakthrough was when he won silver medal at the 1999 World Championships in Athletics in the Olympic Stadium, Seville, Spain with a personal best of 8556 points finishing behind gold medallist Tomáš Dvořák of the Czech Republic. Macey was the inaugural winner of BBC Sports Personality of the Year Young Personality in 1999.