Martin, 30, has been training for more than three years to swim 3,500 miles from New York to Brest in France, The Daily Telegraph reported Sunday.
The swim -- the first stage of his 18-month "global triathlon" -- will take him between four and six months, Martin estimated. Then, once he reaches France, he plans to bike across Europe and through Siberia. Finally, he will run across North America and Canada, back to New York.
Martin said he put on the extra weight while training to help defend himself against the Atlantic's cold temperatures. He said he has been eating four meals a day with 3,500-calorie energy drinks.
While in the water, Martin will be accompanied by the Ice Maiden, a 50-foot research yacht, with a five-person team to supply him with fluids and snacks. He will swim for about 8 hours a day and sleep aboard the yacht.
The only other person to successfully swim across the Atlantic was Benoit Lecomte, a Frenchman, in 1998, which he accomplished in 73 days. However, Lecomte slept on a drifting boat each night, which helped him cover more distance. Martin said he plans to use a GPS device each morning to return to where he finished the previous night.
"I am fluctuating between excitement and nervousness," he said, adding, "The thing I'm looking forward to most is feeling sand under my feet as I land in France."
Martin will set out on his journey this month.