The men's 400 metre freestyle event at the 1956 Olympic Games took place between 1 and 4 December. This swimming event used freestyle swimming, which means that the method of the stroke is not regulated (unlike backstroke, breaststroke, and butterfly events). Nearly all swimmers use the front crawl or a variant of that stroke. Because an Olympic-size swimming pool is 50 metres long, this race consisted of eight lengths of the pool.
Five heats were held; the swimmers with the fastest eight times advanced to the Finals. The swimmers that advanced are highlighted.
Key: WR = World record