The men's 400 metres at the 2012 IAAF World Indoor Championships took place March 9 and 10 at the Ataköy Athletics Arena. The final was won by Costa Rican Nery Brenes in a time of 45.11.

The 2012 IAAF World Indoor Championships in Athletics was the 14th edition of the global-level indoor track and field competition and was held between March 9–11, 2012 at the Ataköy Athletics Arena in Istanbul, Turkey. It was the first of four IAAF World Athletics Series events in 2012, which includes the World Race Walking Cup, the World Junior Championships and the World Half Marathon Championships.