John Bishop says his Sport Relief Challenge will push him to the limits, calling it "the biggest physical challenge of my life".
The comedian will take on 'Bishop's Week Of Hell' - a five-day challenge to cycle, row and run more than 290 miles from Paris to London, starting on 27 February.
Bishop explained: "I must be mad. I'm a man in my mid-40s, a bit thicker round the middle than I'd like to be and I'm about to take on the biggest physical challenge of my life.
"Up until a few weeks ago I'd never even sat in a rowing boat and now I've got miles of water to cover, then there's the cycle and don't even mention the word marathon to me."
Bishop will start the first leg of his Sport Relief challenge by the Eiffel Tower in Paris, before cycling more than 185 miles to the coast in less than 24 hours. For the second leg, Bishop is hoping to row from mainland Europe to the UK - an ambitious task for someone who suffers with bad seasickness.
To help him navigate the choppy waters and battle the waves he will be joined by a team of celebrity rowers, including Davina McCall and Denise Lewis.
The final stage of this epic triathlon will see Bishop take on three exhausting marathons in three days, finishing at Trafalgar Square in London on Friday 2 March.
To help him along, Bishop will be joined on parts of his running leg by celebrity mates including Dermot O'Leary, Frank Skinner and Robbie Savage, who will provide much-needed motivation.
Bishop, who hopes to raise enough money to pay for a vaccine against five deadly diseases for 250,000 children in Africa and also help people in the UK, added: "I know there will be times during the challenge when I'll be freezing cold and fed up.
"But when I'm down I will think back to the people I met in Sierra Leone earlier this year and I'll know every penny I raise really will make a massive difference to people's lives."
Bishop's challenge will be captured for a BBC documentary, to be broadcast in the build up to the Sport Relief Weekend, which is taking place from Friday 23 to Sunday 25 March.