The 28-year-old has not seen his relatives since fleeing in 1993, when the only time he ever ran was to save his life.
But they will try to pick him out among the 109 marathon runners pounding the streets around Buckingham Palace, wearing his specially-arranged Olympic kit.
Marial was born in what was then Sudan but who fled to the United States after 28 members of his family were killed in the conflict. He has a resident’s permit but no passport.
He found out just a week before the Games that he could compete as a rare Independent Olympic Athlete.
“I feel so fortunate to be here,” he told reporters Friday.
“I’m looking forward to the marathon. I wanted to take this opportunity to raise awareness of refugees all around the world and all people who do not have a country. And to the people of South Sudan especially.
“To run under the Olympic flag is a great feeling. Representing the five rings is the best. So I’m representing the whole world.”
Marial arrived in the United States on July 19, 2001, settling in New Hampshire, and now lives in Flagstaff, Arizona, where he largely trains on his own.
As a young country, South Sudan does not yet have a national Olympic committee, and in any case, Marial does not have a passport.
Back home, having no electricity, his family will walk to Panrieng to watch him compete.
“They will be watching me on TV. The nearest city is about 30 miles. They will walk there. At the moment in South Sudan it’s the rainy season so there’s no vehicle,” he said.
“There’s no official road where a car or vehicle can go to the village so they will walk.
“I just want to tell them that I love them so much and I’m here for them.
“I hope the young generation in South Sudan will see me and they will dream high for the next period to come, they will work hard and say ‘we can also get a chance in the Olympic Games’.” – Sapa-AFP