Christian commentator and priest Dr Giles Fraser will be running the London Marathon this Sunday in support of Christian Aid partner Theatre for a Change.
Proceeds will go to helping women trapped in sex work in the illegal settlement of Old Fadama in Ghana.
In addition to poor standards of living, the women suffer physical and sexual abuse and extremely poor health.
Theatre for a Change provides workshops to build the women's self-confidence and reduce their financial dependency on sex work by training them in income generating skills.
Dr Fraser, priest-in-charge at St Mary's Newington in London, said he had been moved by seeing the project first hand: "I've seen what a horrible place Old Fadama is – and to be able to help empower the most vulnerable people there is a privilege.
"This project helps people to think differently. Evidence from similar projects has transformed lives. Women, who were once as low as they could go, have been able to make presentations and lobby presidents. It's very powerful."
Joining Dr Fraser in the challenging run is Mark Ravenhill, the Royal Shakespeare Company playwright in residence and co-creator of new British sitcom Vicious.
Mr Ravenhill said: "I've been HIV positive since 1989 and on anti-retroviral medication since 1997 so the issue of HIV prevention, treatment and of course theatre are all things I care very much about.
"The opportunity to give my 46 year old middle aged body a fitness 'spring clean' plus raising money for a good cause were great motivation for marathon training."
The money raised by the two will also enable women involved in Theatre for a Change to access HIV tests and medication.
Patrick Young of Theatre for a Change said: "The sex workers in the Old Fadama settlement are some of the most marginalised women and girls in Ghana. Money raised from the marathon can help empower them to get out of the physical danger they're in and into a different and more sustainable line of work."
Both men are running the London Marathon for the first time and neither are natural athletes.
Dr Fraser, 48, admitted it was going to be tough: "I was doing really well up until November when I managed 17 miles, but I had some knee problems and training hasn't being going so well since then. I won't be humiliated if a banana passes me on Tower Bridge."
Mr Ravenhill, 46, agrees it's not about speed but making it to the finishing line.
"I've never done any running before in my life but I've been training since June with trainer Alison Harrow at Tigger London," he said.
"The training is hard but I treat it like a job and put the hours in. Still, I'm a slow runner and am expecting to do it in about five and a half hours. I'll carry on training and hope to do marathons in future years at greater speed. But at the moment I'm just concentrating on getting to the finishing line."
People can support Mark and Giles at http://www.justgiving.com/tfac
Watch Theatre for a Change's film for Project Inspire in Old Fadama: