Local athlete Sally Gunnell says Brighton is crying out for a marathon
Brighton's first marathon will be held next April with places for up to 12,000 runners.
Former Olympic champion and local athlete Sally Gunnell launched the event on Tuesday alongside athletes taking part in London 2012.
Athlete and organiser Tim Hutchings said it was a massive logistical undertaking in a city next to the sea which was "very, very hilly".
He said the event would be a "mini-London marathon" and open to everybody.
He said organisers had come up with a course that would take runners through the city and then on to the coast roads during the morning, so that Brighton could function as normal.
Organisers want as much fun during the Brighton marathon as in London
The event was still 10 months away, so anybody who wanted to join in had time to get fit, he added.
He said: "You look at the shape and size of the people who run the London marathon every year, and you realise it's a sport that embraces everybody.
"We want the Brighton marathon to be, in effect, a mini London marathon.
"That means we want all the fun and pompoms and noise and celebration along the course that London offers and we want it to be open to everybody."
The marathon website, which includes a map of the course, said the 26-mile route on 18 April 2010 would be generally fast and reasonably flat, taking in glorious coastal views, but keeping disruption to a minimum.