The staggering challenge will see Eddie run over 700 miles in temperatures of up to 30°C without a day off.
The new BBC Three will exclusively cover Eddie’s journey from his first marathon on 23rd February to his last marathon on 20th March.
Eddie has chosen to run 27 marathons to reflect the 27 years that Nelson Mandela spent in prison.
Throughout his journey he will explore the history of South Africa and Nelson Mandela as well as visiting organisations and families that have been helped by the work of Comic Relief.
Eddie’s mammoth undertaking will culminate in Pretoria on Sunday 20th March, at the same time as the Sport Relief Games will be taking place across the UK.
The challenge will be an important one for Eddie as he had to pull out of a similar feat in South Africa in 2012 for health reasons. That attempt followed his fantastic effort for Sport Relief in 2009, when he completed 43 marathons in 51 days across the UK, raising over £1.8m.
The money raised from the Eddie Izzard: Marathon Man challenge will be used to help transform the lives of some of the most disadvantaged people both at home in the UK and across the world’s poorest communities.
“Eddie is undoubtedly one of our Sport Relief legends, and we are absolutely thrilled that he is going to push himself to the physical limit once again,” Kevin Cahill, Chief Executive at Comic Relief, said. “What he did for Sport Relief last time was truly astonishing and raised a staggering amount of money that has really helped to transform lives at home and across the world. We are beyond grateful for his continued support and will be with him every step of the way.”
BBC Three, which launches on Tuesday 16th February, will document Eddie’s progress every step of the way via its new digital and social channels.