As he crossed the finish line, the double leg amputee slumped in his kayak in a moment of exhaustion, relief, and reflection.
The reigning world champion said the enormity of what he'd achieved wouldn't sink in until he got home.
"I'll drink some decent coffee and reflect on the wounds that have healed and the people that have helped me get here," he said.
McGrath lost his legs four years ago when he stepped on a landmine while serving in the Australian Army in Afghanistan.
Despite fighting shock, blood loss and excruciating pain, it was McGrath, as the first-aid medic for his unit, who instructed the soldiers around him to perform first aid.
As he was being airlifted to safety, the then 24-year-old made a vow to the men who helped save his life that they would see him see him represent his country again, not on the battlefield, but on the Paralympic sporting field.
McGrath was neck and neck with Swoboda until the halfway point of Thursday's final, but powered home with his signature strong back end.
"It's actually a carbon copy of our race in the world champs this year," McGrath said.
"He's ahead at the 100m mark and I gradually kick into another gear and cruise over."
The Queenslander has big plans for the future.
"I'd like to go to Tokyo, pick up another sport, but we'll see how we go," he said.
For now, he wants to grow the debut sport of para-canoe and the Paralympic movement.
"There's many more disabled athletes or potential athletes that could be out here and get to the world stage," he said.
- AAP