During his mission to explore the dark, freezing waters of the Challenger Deep in the Mariana Trench, around 320 kilometres from the Pacific island of Guam, Mr Cameron found few signs of life apart from some inch-long prawn-like creatures.
Using a specially-designed submarine, he became the first person ever to cast eyes on depths of 35,576 feet below the ocean’s surface.
An earlier manned mission in 1960 involved no observation because the craft kicked up too much sand from the ocean floor, reducing visibility to zero.
The Titanic and Avatar director also suffered mechanical issues during his three-hour sojourn on the deepest ocean bed in the world, and was forced to cut his trip short when hydraulic failure meant he was unable to carry out his plans to collect samples.
All but a small amount of silt was washed away on his ascent back to the surface.
But Mr Cameron nevertheless described his mission as a huge success — and the start of what would be a series of journeys to explore the Mariana Trench, which is larger than the Grand Canyon and as deep as Mount Everest is tall.
“It was very lunar, a very desolate place, very isolated,” he said.
“My feeling was one of complete isolation from all of humanity.
“I just sat there looking out the window ... and appreciating it.
“It’s very different than kind of what you imagine. You have to go through it, you have to really experience it.
“It’s really the sense of isolation, more than anything, realising how tiny you are down in this big vast black unknown and unexplored place.”
Mr Cameron said that while everyone had been hoping to find “sea monsters” below the surface, even he had been surprised at the barren nature of the ocean’s depths.
“I didn’t see anything bigger than about an inch long,” he said. “I didn’t see fish. The only free swimmers I saw were these amphipods, which are shrimp-like.
“I didn’t feel like I got to a place where I could take interesting geology samples or found anything interesting biologically.
“It was absolutely the most remote, isolated place on the planet. I really feel like in one day I’ve been to another planet and come back.”
The specially-designed lime-green craft, called the Deepsea Challenger, was designed to withstand the enormous pressure levels - the equivalent of eight tonnes per square inch - at the bottom of the Challenger Deep, the deepest part of the Mariana Trench.
It has a small passenger container, which heats up to above 100 degrees Fahrenheit at the start of the dive due to the amount of electronics on board, before the temperatures inside the capsule rapidly plunge to near freezing as it enters deep waters.
Mr Cameron insisted he was not disappointed by the failure to capture samples. “Every time you dive, you hope you’ll see something new some new species. Sometimes the ocean gives you a gift, sometimes it doesn’t,” he said.
“But I call this dive just the first phase. We prove that the vehicle works, and hopefully bring some real science back.”
Describing his experiences on the ocean floor, he said: “I landed on a very soft, almost gelatinous flat plain. Once I got my bearings, I drove across it for quite a distance ... and finally worked my way up the slope.
“When I was in the New Britain Trench a couple weeks ago, the bottom was covered in the tracks of small animals, which gave it an eggshell appearance.
“But when I came to Challenger Deep, the bottom was completely featureless. I had this idea that life would adapt to the deep ... but I don’t think we’re seeing that.”
“I see this as the beginning ... of opening up this frontier to science and really understanding these deep places.”
Recalling the experience of plunging into the deep, he added: “When you first close the hatch, all these electronics are dumping heat into the sphere.
The Mariana Trench, the deepest point on Earth, is marked with a red 'X'
“But as you start descending, the sub goes very fast. I’m screaming down, and in just a few minutes I’m in water that’s 36 degrees Fahrenheit [2.2 degrees Celsius].
“All of sudden my feet are freezing, the back of my head is freezing, but the middle part of my body is still warm.
“Literally within a minute or two I’m out of sunlight, and you’re in total darkness for most of this dive, so the sub gets very cold, and you have to put on warm clothing. ... The walls have condensation all over them and I’m constantly getting dripped on by cold water.”
Mr Cameron also disclosed that delays to the start of the dive, caused by poor weather conditions, meant that he might miss the London premier of Titanic 3D. “It was like the ocean presented me with a choice,” he said.
But he vowed that his continuing interest in sea exploration would not limit his cinematic pursuits — he is due to begin filming Avatar Two and Avatar Three soon.
Sir Richard Branson, the entrepreneur and adventurer who is planning his own deep sea dive this year, congratulated the Canadian-born Mr Cameron.
He said: “What he has achieved is fantastic. Hundreds of people have now been into space, but he is only the third person to go so deep below the ocean’s surface.
"It’s a fantastic example of human endeavor and determination."