The beauty is joining her clothing designer pal Henry Holland, British actress Emma Pierson, and model David Gandy in the 'Oxglam Squad', which aims to raise cash for anti-poverty charity Oxfam.
Deyn is running the 26.4-mile (42.2-kilometre) course with the team, which was put together by fashion photographer Rankin. The marathon takes place on 17 April (11).
She says, ""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.""
British singer Will Young and The Hoosiers frontman Irwin Sparkes have also signed up to take part in the marathon.