He was on his fourth day of a t our in Afghanistan with the 1st Battalion Scots Guards when an explosion blasted away both his legs and his left arm.
He almost didn't survive, but was saved by his comrades' quick actions.
After six days in a coma, then undergoing treatment at the military hospital in Selly Oak, Birmingham, and then Defence Medical Rehabilitation Centre at Headley Court, Sussex, he pulled through.
Prime Minister David Cameron even paid tribute to his bravery in Parliament.
Finally, about 200 residents welcomed him home to Stonehouse, Lanarkshire, that July with a hero's party.
But it is thanks to Ideal Homes For Heroes that he was able to go back to the family house at all.
Just getting through the door would have been impossible without its help. Changes put in by the charity include a wider front door for the wheelchair he still needs, as well as larger doorways inside, level paving outside so he can use the back door, a stairlift and a wet room with a shower.
They even provided hotel accommodation for the family, including his children Tayln, 3, Kyle, 12, and Nicole, 16, while the work was being done.
The charity also paid for Gary's car to be adapted and he finally got back behind the wheel a year ago.
He said: "It's awesome. The charity has always been there, but I never expected to use it.
"It has made a big difference. I didn't have to go buy a house that was modified. We probably would have had to move.
"When you come back, you want to come back to normality.
"I couldn't get in the house because the front door step is quite steep. Then I had to sleep downstairs until we got a stairlift."
His wife Claire, 34, said: "Gary couldn't get in any of the doors, so getting those changed was a big must. We have been here 10 years and wanted to stay."
The Ideal Homes For Heroes appeal, which is now in its third year, has raised more than £360,000 and has helped more than 1000 people.
Managed by the Army's national charity, ABF The Soldiers' Charity, it aims to raise £1million by 2014. And charity bosses hope to gather £20,000 in Glasgow over the next four days, including a cut of the ticket price from the Ideal Home Show at the SECC.
While Gary's house is now fit for a hero, he is getting over a setback in his recovery that he says has been harder than losing his legs in the first place.
Although he was walking on prosthetic six months after the accident, he is temporarily back in his wheelchair.
He returned to Headley Court a few weeks ago to be fitted with new legs. But surgery to reconstruct his right stump – because his prosthetic leg kept falling off – saw him pick up an infection.
The 32-year-old said: "After the blast the stump wasn't a normal shape, so the surgeons made it rounder. It was tidying up surgery. But my leg got sorer and sorer.
"Going back to a wheelchair is quite hard. It's probably harder than being blown up at first. When you are finally walking and then have to go back into a chair it's hard.
"One of the things that has been hard is not having the freedom to go anywhere.
"A lot of places say they have disabled access but, well, they don't know what disabled is.
"You can get in but the toilets will be upstairs. We need to pre-plan everything now."
He says he thinks about the blast that changed his life only when he is asked to talk about it and his main memory of it is the image of Tayln, then a baby, in his head.
He said: "At first, when the bomb exploded, I laughed in my head. Then I tried to sit up and realised my legs were away. I was in no pain whatsoever.
"The initial 30 seconds I thought I was dying, but then a picture of baby popped into my head and that was me.
"And when you hear the chopper coming you think 'I'm fine now.' It took 18 minutes from the blast."
Sadly, Gary's comrade Alan Cameron, 42, from Livingston, who was injured alongside him, died a year later.
But Gary is now looking to the future. He is being discharged from the Army in June next year and is hoping to line up a new career.
He is interested in getting a job in one of Lanarkshire's distribution centre and hopes to start doing work placements to prepare soon.
Long term, the couple hope to emigrate to Australia, but before that they are off on a holiday to New York with Army friends.
Gary is also planning a charity dinner and auction at South Lanarkshire Council's headquarters in Hamilton on October 5 to raise money for charities that have helped him.
One thing that will be hard will be waving his battalion off to Afghanistan again in October.
He said: "I'm gutted I'm not going with them. When you're in the Army, it is part of your job."
l The Ideal Homes Show Scotland runs from today until Tuesday at the SECC. Tickets, £12 in advance, or £15 at the door. See the website: www.idealhomeshowscotland.co.uk/ticket-information