DUP veteran Gregory Campbell has said that the work of the Pat Finucane Centre (PFC) has been called into question after the group's director admitted he had been a member of the IRA.
Paul O'Connor told The Irish News that he joined the IRA as a 15-year-old in 1970.
The revelation comes just one day after the human rights organisation strongly denied he had ever been a member.
While he admitted being a member of the IRA Mr O'Connor claimed that he "did not create victims".
Mr Campbell said that that "virtually all" of the PFC's work centered on the actions of the state and its forces including the Army, UDR and Royal Irish Regiment.
"Questions now need to be asked after the main architect of many of the PFC's reports has revealed that he was once a member of the IRA," the DUP Westminster candidate for East Londonderry said.
"How can these PFC reports be trusted as unbiased after this admission? That's for them to reconcile.
"This man claimed to be a human rights activist when really he was a member of the organisation that created more victims than all of the other organisations involved put together. The irony of that will not be lost on people."
Mr Campbell said that Mr O'Connor offered no apology for his membership of the IRA and called on him to reveal exactly what he done while a member of the organisation.
"He should apologise unreservedly to victims who will have been retraumatised by his admission," Mr Campbell said.
Victims' campaigner Kenny Donaldson said that Mr O'Connor was not the only former paramilitary involved in victims' groups in Northern Ireland.
“There are groups funded to support victims and survivors who feel it is acceptable to employ those with past involvement in terrorism," the South East Fermanagh Foundation's Director of Services said.
“We don’t employ perpetrators, we don’t have perpetrators as volunteers and nor do we have perpetrators as beneficiaries - we are a group supporting innocent victims"
Mr Donaldson said that Mr O'Connor's admission meant there were questions to answer around his continued involvement with victims.
He said that he had not expressed any remorse or willingness to account for what he had done.
"Several questions need posed; are the PSNI now going to question Mr O'Connor in respect of his admission of Provisional IRA membership? And are there issues for organisations around compliance with ACCESS N.I regulations concerning them working with and supporting vulnerable adults and children?," he said.
"Because someone has a past does not mean that they cannot have a future. We need openness, transparency and a willingness to account for wrong, sadly this remains missing across our society and community."
TUV leader Jim Allister said that Mr O'Connor had spent years hiding his membership of the IRA.
"This is a man who has spent many years trudging through government papers attempting to rake up the past and now we discover that he has a secret IRA past of his own," the North Antrim MLA said.
"I think that says it all about the Pat Finucane Centre.
"He claims to represent victims and he now admits he was a member of an organisation that created victims."
The allegations around Mr O'Conor's IRA membership came to light earlier this week after former IRA man Shane Paul O'Doherty published a blog claiming he had been a teenage friend of Mr O'Connor and that they had been sworn into the organisation together as 15-year-olds in 1970.
Mr O'Connor rejected a claim from Mr O'Doherty that he had been present when an IRA member was shot in Londonderry in 1971.
Mr O'Doherty was jailed for 15 years for his part in a letter bombing campaign, but has since renounced his IRA past.
He claimed that Mr O'Connor had been present when 16-year-old Jim O'Hagan was shot by another IRA member in 1971 and that Mr O'Hagan had been taken to Mr O'Connor's family home where he died.
Mr O'Connor denied being present when Mr O'Hagan was shot but confirmed he was there when he was brought to his home.
The PFC director said that Mr O'Hagan was taken to hospital where he died.
Mr O'Doherty also posted a picture of a young man with an Armalite rifle he claimed was Mr O'Connor.
While he said he had no recollection of the photo, Mr O'Connor did admit that "it is reasonable for people to look at the photo and say that looks like Paul O’Connor”.
Mr O'Connor denied taking part in an IRA bombing campaign of Derry city centre and said he was told to leave the organisation in 1972 for disobeying orders.
“I did not create victims, that is absolutely clear, none,” he said.
After leaving the IRA Mr O'Connor lived in Germany and the US before returning to Derry in the early 1980s and beginning his role as a campaigner and activist.
The PFC is a registered charity and describes itself as a "a non-party political, anti-sectarian human rights group advocating a non-violent resolution of the conflict on the island of Ireland".
It represents Troubles victims and receives funding from a wide range of organisations, including the Irish government and European Union.
Mr O'Connor acknowledged that his IRA past could bring his role with the PFC into question.
“Clearly it is in the public domain. People are saying the PFC has questions to answer. Why am I doing this right now? I think I owe it to the families we work with," he told the Irish News.
“I have talked to a number. I think it is only right to do something. I don’t know how all the families – and they, along with Jim’s family, are the most important – are taking this; how must it has impacted on them.
“For those who say you cannot work in the PFC because 48 years ago you were in the IRA, I have to leave that to the staff and families. I would ask people to judge me on what I have done throughout my entire adult life."
The Pat Finucane Centre has been contacted in relation to Mr O'Connor's admission.