In a special event to raise the profile of the next Olympic games, triathletes will start the first leg of a three-pronged race in Paris and finish the course in London, having gone via Brussels.
The swimming event will be staged in the French capital and the athletes will then board the Eurostar to Brussels where they will take part in the cycling leg.
Another Eurostar trip will see the triathletes finish their event with the run in London.
It is part of Eurostar’s third level sponsorship of the London Games where the firm will be the official international rail services provider.
Lord Coe said: “We have got a Tri-City-Athlon which is at the coal face of helping young people understand what Olympic sport is about.”
Eurostar expects to carry more than one million people to participate and watch the Games.
On the value of having Eurostar on board, Lord Coe said: “We know that a large part of the way you arrive at a Games, how you are treated and the level of service provision shapes a large part of the rest of the trip.”