Victims' groups, in particular the US-based Survivors Network of those Abused by Priests (SNAP), have criticised the formation of the commission, which now totals 17 members, as a meaningless gesture, likening it to "offering a Band Aid to a cancer patient."
But Mr Saunders, the founder of The National Association for People Abused in Childhood, said he was cautiously optimistic that the papal commission could lead to tangible reforms.
"I think the Church is changing – it certainly needs to – and Francis is the right man for the job at this time," Mr Saunders told The Telegraph. "I believe him to be sincere. Let's give the process a chance.
Mr Saunders, 57, who still has regular therapy for what was done to him as a child, was one of six victims who met the Pope at the Vatican in July.
He was forthright about the appalling abuse he had endured.
In addition to the two Jesuit priests, who also molested his brother, he was sexually abused by the head teacher of his primary school in New Malden, London, as well as by a family member. Even after the teacher was exposed as "a serial child abuser", he was simply transferred to another Catholic school within the diocese, rather than being sacked and reported to the police.
"I told the Pope what had happened to me and said that the Church must get its act together, otherwise it will be in big trouble," said Mr Saunders, who remains a devout Catholic despite what was done to him. "I'll be asking what concrete steps we can help the Church to take."
"The Pope wants the commission to answer directly to him and that's amazing. If the top man wants to hear from the horse's mouth, then I think that is a huge step," said Mr Saunders, who has two grown-up children, three stepdaughters and four grandchildren.
At the meeting in July, the Jesuit Pope, who turned 78 on Wednesday apologised for the Church's complicity in what he called "execrable acts of abuse which have left lifelong scars".
Campaigners from SNAP said that rather than setting up the commission, the Pope needed to immediately start defrocking bishops found to have covered up abusive clergy.
"As long as Catholic officials can pretend they need more information or advice, they can keep making excuses for refusing to take real steps to protect children," said David Clohessy, a director of the pressure group.
Mr Saunders will travel to Rome in February for the first full meeting of the commission. One other member is British – Baroness Sheila Hollins, a psychiatrist and a former president of the Royal College of Psychiatrists and the British Medical Association.
The panel includes an Irish survivor of sex abuse by priests, Marie Collins, who has been an outspoken campaigner on the issue.