Mervyn Thomas, head of Christian Solidarity Worldwide (CSW), says he is scared of heights but was taking on the challenge to raise money for persecuted brothers and sisters.
Raising somewhere between £3,000 and £4,000, he afterwards acknowledged: "I think it was the most nerve-wracking thing I have ever done."
Speaking before the challenge, he told Premier's Big Breakfast said: "It is 249 steps up the tower and 160ft down. Somebody sponsored me one pound for every step up and one pound for every foot down. People have been very generous.
"This is the last thing in the world I want to do. I suffer from vertigo but - when I think of what people go through in other parts of the world - for my few minutes for nervousness, it's nothing. It's well worth the while."
There he goes! Good luck Mervyn! #CSWabseil2016 pic.twitter.com/OgpxootYiP
— CSW_UK (@CSW_UK) June 4, 2016
CSW works for religious freedom all over the world through advocacy and lobbying.
On his fund raising page Mr Thomas wrote: "Did you know that 75% of the world's population live with severe restrictions on their religious freedom?
"This means that 75% of the population isn't fully free to practise, talk about and choose their own religion.
"In Pakistan this could look like a young woman being forced into marriage, in Cuba it could look like a church torn down, in Nigeria it could look like a village destroyed.
"At CSW we want to see this change! We dream of a world where individuals are free to live out their faith in safety and in peace with those around them, despite religious differences."