Mellouli, who won gold in the 1500m free at Beijing 2008 and 10km at London 2012, had been considering retirement during a long break from the pool in Tunisia.
He won bronze in the 1500 in London.
"I want to make the World Championships, which mark the 10th anniversary of my first medal at the World Championships in Barcelona in 2003," he told AFP.
"I want to do the open water and the 1500m too."
Mellouli, 29, was the first swimmer to win Olympic titles in both the pool and open water, having taken the latter up recently.
"After London, I said that I was ready to go out the door. But I reassessed my situation and set new goals around my new passion, open water," he added.
"It's nice at my age and after the career I have had to have this kind of stimulus."
Mellouli has trained in Los Angeles since 2002, where he is studying for a Masters in Sports Management.
He began his break immediately following London 2012.
"I have maintained my figure, but I'm not in intensive preparation," he said. "Four months before the Worlds I'll look at things and consider beginning the Olympic cycle again seriously."
The Worlds are to be held from July 19 to August 4.
Mellouli won the 2009 world title in the 1500m free. He also has a pair of silver and another pair of bronze long course World Championship medals, all over shorter distances.
- Sports & Recreation