Marine Cpl. Kionte Storey and his unit were on patrol in Helmand Province, Afghanistan, when he stepped on an improvised explosive device in 2010.
He lost his right leg below the knee and suffered damage to his left leg. He told ABC News' David Muir on Tuesday that he experienced some dark days as he recuperated from his injuries.
Then one day, Storey said, he took a hard look at himself in the mirror and made a decision.
"I was going down a dark hole that I didn't want to go down," he said. "I just realized for me, it wasn't me ... I wanted to make that change."
Storey, 29, said he stopped taking his pain medication and got involved in sports, joining teams with other veterans. He said he focused on challenging himself physically and mentally.
"[It] kind of just went uphill from there," he said.
On Tuesday, Storey spoke at the annual Stand Up for Heroes benefit, presented by the New York Comedy Festival and the Bob Woodruff Foundation. The foundation was created by Woodruff, the ABC news anchor injured in Iraq in 2006.
Stewart told Muir Tuesday that the event was like a yearly get-together.
"You get to see people progress through their recovery ... You follow through their ups and downs and it becomes personal," he said.
Since his injury and rehabilitation, Storey has run track in the Paralympics and completed the Marine Corps Marathon. This summer, he reached the top of Mount Kilimanjaro in Africa, in collaboration with the Bob Woodruff Foundation and the #Give2Veterans campaign.
He told Muir that his biggest highlight since losing his leg, however, was reaching the summit of Mount Vinson in Antarctica in 2013.
"To realize why you're doing what you're doing and really understand that 'Why?' factor. ... [It] pushes you to keep going and never quit no matter what you're doing," Storey said.
The next Woodruff Foundation fundraising event, "Dine Out for Heroes," will be on Nov. 11 in New York City. Visit bobwoodrufffoundation.org for more information.