Ireland's Marie Collins explained the reasons for her resignation
in a statement published by the National Catholic Reporter
Collins was the only currently active member of the commission who also was a victim of abuse.
In February 2016, Peter Saunders -- the other member of the commission to have been sexually abused by a priest -- was suspended after publicly criticizing Vatican cardinals and bishops for blocking progress on transparency in clerical sex abuse.
"It is a reflection of how this whole abuse crisis in the church has been handled: with fine words in public and contrary actions behind closed doors," she said in her statement. Collins said that one Vatican office had even refused a papal directive to respond individually to all correspondence from victims and survivors.
Pope Francis understands 'horror' of abuse
Collins said that guidelines for safeguarding children and vulnerable adults from abuse, developed by the commission, were never disseminated by Vatican offices to bishops around the world.
The Vatican had no comment Wednesday.
Referring to recent accusations that Pope Francis may be too lenient in punishing priests guilty of sexual abuse, Collins said in the statement that the Pope "does not appreciate how his actions of clemency undermine everything else he does in this area including supporting the work of the commission."
But she said she believes that "at heart" Pope Francis understands "the horror of abuse and the need for those who would hurt minors to be stopped."
Collins' statement also cited a lack of resources, inadequate staff and cultural resistance as stumbling blocks to the commission's work.
"However, despite the Holy Father approving all the recommendations made to him by the Commission, there have been constant setbacks," the statement said.
"While I hope the Commission will succeed in overcoming this resistance, for me it is the last straw."
The Commission for the Protection of Minors -- headed by Boston Cardinal Sean O'Malley -- was established in 2014 to advise Francis on best practices in protecting minors and vulnerable adults.
Abuse victims disappointed by resignation
Victims of clergy sexual abuse reacted to Collins' resignation with dismay.
"The fact that she has quit has exposed the depths of the problem," said Barbara Dorris, outreach director for the Survivors Network of those Abused by Priests.
"The most frightening part is there's no real effort to protect the children," she said. "The Vatican says, 'we'll create a tribunal, a commission', but there are no real actions that go with that.
"The predators are with the kids," Dorris said.
"Pope Francis should respond by firing all the Curia department staff who refuse to implement or delay programs that protect children," Donna B. Doucette, executive director of Voice of the Faithful, said in a statement.
"The Church cannot ignore modern-day prophets like Marie and still claim to care about removing clerical sex abusers," Doucette said.