Former western-Sydney MP and ultra-marathon record holder, Mr Farmer is running 4,600 kilometres from southern Indian port of Kanyakumari to Kashmir in the north.
He's aiming to raise $100,000 dollars for the education of girls in India, where fewer than 65 percent of girls can read.
He set out on India's Republic Day, January 26, with hundreds of supporters at the starting line.
Mr Farmer told SBS ahead of leaving for India that the marathon is a challenge he's excited to embrace.
"I love the feeling of freedom when I get out to various parts of the world and see things through my own eyes that a lot of people only imagine,” he said.
"If they can't read or write then often all the family is put back and I always say if you educate the girl you educate the nation."
Mr Farmer is hoping to complete the run 46-hundred kilometres in about 60 days.
Starting from southern-most point of India, he'll run along the west coast, towards Mumbai.
Covering about 80 kilometres a day, he will pass through Delhi, ending at the foothills of the Himalayan mountains.
In 2011 Mr Farmer ran a nine month marathon from the North Pole to the South Pole, and in 2014 he undertook a peace run from Lebanon to Israel.
Former federal Liberal MP Pat Farmer in Antarctica, during his record run from the North to South Pole. Source: AAP
Mr Farmer is expected to finish the sea to summit marathon by the end of March.
