Marial competed in the marathon on Sunday as an independent runner under the banner of the International Olympic Committee after fleeing a refugee camp in what is now South Sudan during a civil war more than a decade ago.
While other runners wore the colours and ran under the flags of their countries, Marial wore a predominantly black and grey uniform with "I.O.A." printed on the chest. He finished 47th, 11:31 minutes behind the winning time.
The time was of little consequence.
"Finishing the marathon is more important than anything like that," he said. "This is special for the people who support me, in the United States and the whole world and my people in south Sudan. It was important for me to finish, no matter what."
After fleeing the civil war, Marial, now 28, landed in the United States, seeking asylum. The IOC cleared him last month to compete in the Olympics as an independent athlete after he didn't qualify for Sudan, South Sudan or the United States under its rules.
Not having a flag "doesn't worry me a lot because coming here, technically, I feel like I was representing South Sudan even though I was not wearing it," he told The Associated Press immediately after the marathon. "It is important to bring the name of south Sudan here and raise awareness of the issue going on in South Sudan.
"I just wanted to compete as an athlete because the love of the country is very important for me. I was not able to get them a medal ... but, I felt like the world was watching."
Marial was born in what is now the newly independent country of South Sudan. He fled a long time before the south broke away from Sudan last year and doesn't have any South Sudanese documents. Although he is now a permanent resident in the U.S., he's not a citizen there either.
He was offered the chance to represent Sudan at the games but declined.
With no passport, no country and seemingly no hope, Marial met fellow runner Brad Poore at a race in Minneapolis in October and 10 months later — with plenty of help from his new friend — he got to compete on the final day of the London Olympics.
Marial had run only two marathons previously, but finished both in Olympic qualifying times. His second was just two months ago in San Diego, leaving him very little time to taper for the biggest race of his life.
"It was a heavy responsibility on my shoulders, but it was great," he said. "I feel blessed to be able to do this. Two marathons back-to-back in two months was not ideal. The whole thing is to do this to honour our people. Support the refugees and the people of South Sudan."
Thousands of people lined the marathon route, which wound past many of London's famous landmarks and finished in the Mall, within sight of Buckingham Palace. He saw people waving south Sudan flags, and yelling encouragement to him in his native tongue. And he heard plenty of other support from the fans who have followed his story.
For that, he was grateful to the IOC for helping him get to London.
"The IOC is great. It's special. I can't thank them enough for giving me this opportunity," he said, touching the small I.O.A. letters on his chest before pounding the other side. "At the same time, It's about the people. In my heart here, I'm carrying those people in my heart."