Ben Hooper, 38, is due to begin his 2,000-mile challenge on the west coast of Africa when he sets off from Dakar in Senegal to swim to Brazil’s Natal. He wants to raise £1 million for charity.
People have previously swum oceans, but the full 1,883 miles - the longest stretch across the Atlantic between continents - has never before been officially completed.
French-born Benoit Lecomte was credited as the first to swim across the Atlantic without a kickboard in 1998, but the attempt was not verified by Guinness World Records.
Mr Hooper is taking no chances with his challenge, Swim The Big Blue.
His support boat and crew includes a medic, body therapist and official observer, who will be reporting back to Guinness.
He will be following an even longer route to ensure he properly swims every mile required for the record, allowing for deductions to be made for aspects such as currents.
The former policeman, who was born in London but now lives in Cheltenham, Gloucestershire, will swim for up to 12 hours a day for four months, facing storms and 20ft waves, jellyfish and sharks.
“I think the only real fear I have got is failing,” he said. “If something goes wrong with me physically or mentally or the boat breaks or marine life gets involved or freak weather. The idea is to get across safely and I think my only real fear is if something goes mechanically wrong with me.
“Beyond that I am not too worried about marine life. I am going into their world, so I need to be respectful. I’ve already met sharks and jellyfish and nothing has eaten me yet.
“I just want to complete it and get it done and keep inspiring people and raise £1 million for charity, which is my ultimate aim. That’s another fear - what happens if we don’t raise enough money for charity?”
He decided at the age of five - when he nearly drowned in a swimming pool - that he wanted to swim across an ocean.
This was not his first brush with death.
After being born six weeks premature, he clinically died three times during his first few days due to collapsed lungs, only to be resuscitated each time.
Mr Hooper has been long-distance swimming for years and taken part in amateur triathlons, but has never attempted anything of this magnitude.
For him, one of the final triggers was a severe bout of depression, which ultimately inspired him to change his life.
“When I left the police I had a bought of depression and it came back about three and a half years ago and I thought I had to turn my life around,” he said.
“I had always wanted to do this since the drowning incident and I picked up the phone and Guinness confirmed no one had ever swum every single mile of an ocean. More people have landed on the moon than have even tried this.
“It was there to be done. At that point I told my daughter’s mother in the kitchen that I was going to swim the Atlantic and she said, ‘That’s nice, pass me the tea towel’.
“Here we are three years later - on a beach in Dakar preparing to go.”
Mr Hooper committed himself to a punishing training regime, clocking up countless hours in the pool and the sea, and racking up more than 12 million metres in the water.
He has also taken on extra calories and bulked up as he will consume around 10,000 to 12,000 calories a day during the challenge.
A waterproof MP3 player helps with the solitude and monotony of long stints in the water. And he has also been working with Hartpury College on a pioneering study into the effects of different types of music on athletes’ perceived fatigue and performance.
He added: “The idea of inspiring people is a bonus to turning my life around. I’ve spoken to 11,500 schoolchildren in the UK and US and they love it - even if it is the idea of me being eaten by shark.
“One of my three objectives is to inspire as many people as I can.”