The 28-year-old will join model David Gandy, designer Henry Holland and actress Emma Pierson to run the marathon in a team organised by fashion photographer Rankin, 44, and his wife Tuuli Shipster, 28.
The team, dubbed The Oxglam Squad as they're raising money for Oxfam, will take to the streets of London on April 17 to run the 26-mile course.
Deyn said: 'It's going to be fun running the marathon with Henry and the rest of the Oxglam Squad, and it's also great knowing that Oxfam will put the money we raise to such good use.'