Peter Saunders, 57, was one of six abuse survivors who met with Francis at the Vatican in July, reportedly giving the Argentine Jesuit his first, face to face account of the traumatic toll that abuse wreaks on its victims.
Speaking to the Guardian, Mr Saunders said: "I have been a thorn in the side of the Catholic church for some years. When I was called to see if I would be prepared to meet the pope it didn't take me very long to say yes.
"When I met him in July and started conversing with him, I told him the church needed to get its act together, that it needed to support survivors and to do more to protect children. I said to the pope I would be coming back to see him, but I never dreamed I would be invited back to join his commission."
"He granted me something that the prime minister, and the deputy prime minister and all these other ministers of state in the UK never have. I had the benefit of a discussion with him, with no limits ... It was a life-changing moment for me," he said.
Earlier this month, Saunders, the founder of National Association for People Abused in Childhood, (NAPAC) which represents victims of alleged historical sexual abuse in the UK withdrew its support from the Government's child sex inquiry, claiming it was "not fit for purpose".
The panel, which has started work, still has nobody to chair it after the first two nominations stood down over links with establishment figures.
On Monday, Home Secretary, Theresa May told the Home Affairs Select Committee that the inquiry into historical child abuse should be able to compel witnesses to give evidence, one of several demands set out by alleged victims in an open letter.
The letter also said the inquiry's terms of reference went "well beyond the original declared intentions ... to investigate government and establishment cover-ups of paedophiles in their ranks".
It accused Mrs May of failing to address potential conflicts of interest among members of the panel inquiry, after two people appointed to chair it had to resign for similar reasons.
