Tennis star Andy tweeted his support for his wife Kim's brother as the adventurer set off on Wednesday.
After flying to Chile last week, before heading to Hercules Inlet on Antarctica's Weddell Sea a few days later, Scott said it had been a "mad dash" to get final bits of kit ready.
He said: "I am very excited - it has been two years in the planning so it is nice to finally be under way.
"I'm looking forward to the moment where I finally get chucked out the side of the plane, and I am actually there looking out at the expanse of Antarctica after years of visualising it and dreaming of it."
Lt Sears, who lives in Shoreditch, London, said he hopes to arrive at the South Pole in time for Christmas Day.
He is looking to raise more than £25,000 for the Gurkha Welfare Trust to help rebuild schools in Gorkha, Nepal, destroyed in the earthquake of April 2015.
"We are hopefully going to rename one of the schools after Rifleman Suraj - he was the last member of 9 Platoon which is the platoon I took over - to be killed in Afghanistan," he said.
Braving temperatures ranging between zero and minus 60C as well as 100mph winds, he will walk and ski over crevasse fields, glaciers and the Antarctic plateau.
Admitting his choice of expedition is "a very, very strange life choice", and something which did not initially excite his mother, he said his whole family is now "very supportive" of his trek.
"I used to do quite a lot of mountaineering, but polar travel and polar adventure exploration always appealed to me - a solo expedition is about as challenging as you can get both mentally and physically," he said.
The 6ft 5in former tennis player will burn more than 10,000 calories a day as he pulls a 100kg sledge, also known as a pulk, containing all his food, fuel and equipment.
He said his training has involved dragging tyres down beaches, gym sessions, and trips to Norway and the Arctic to train in cold conditions.
"I am lucky that the Gurkhas are probably the fittest out there, and I have to keep up with them all the time, so I have to stay quite fit," said Lt Sears, who has been in the Army for almost three years.
"We are light infantry so we carry our houses on our back most of the time anyway - so for me it was getting used to dragging rather than carrying."
He will be taking 50 days worth of "quite tasty" dehydrated meals with him, including chicken tikka masala and beef stroganoff, as well as stores of salami and chocolate.
Quizzed on how he will cope with being alone, Lt Sears said once he gets off the plane he will mentally break everything down into "tiny little tasks" to focus on.
Asked how he will stay motivated, he said: "I've got music, podcasts, audiobooks - I have enough memory on my phone to get a couple of series of Narcos on, which I haven't watched yet because I am well behind the trend.
"So I am going to give myself an episode a night, on my phone, in my tent, as I melt my water."
- To make a donation visit http://www.justgiving.com/fundraising/scottsears