Swimming at the 2012 London Summer Games:

Michael Phelps was the two-time defending champion (2004-08) but the favorite was his teammate Ryan Lochte, the 2011 World Champion who had defeated Phelps at the US Trials in June. Phelps had said after Beijing that he would never race the 400 IM again but had started training for it in late 2011. But it was too late for London and he barely qualified for the final, placing eighth and having to swim the final in lane eight. The best qualifying time was posted by Japan's Kosuke Hagino in an Asian record 4:10.01, with Lochte qualifying third.

In the final, Lochte, Phelps and South African Chad le Clos were about even at the end of the butterfly, but the next stroke, the backstroke, was Lochte's best and he pulled ahead by two bodylengths entering the breaststroke. He was under world record pace at that time and although he could not maintain that, he won gold in 4:05.18. The time was the second fastest ever after Phelps' winning Beijing world record of 4:03.84, but it was faster than Phelps' textile world best of 4:06.26.

The silver went to Brazil's Thiago Pereira, over 3½ seconds behind Lochte, while the bronze went to Hagino, with Phelps off the podium in fourth – only the second time this had ever happened to him at the Olympics, after the 2000 200 butterfly, in which he finished fifth.