The largest association of psychologists in the United States voted to begin reversing its policy of collusion in torture on Friday by prohibiting members of the American Psychological Association from participating in the interrogation of US prisoners on foreign soil.

In the wake of a devastating internal report that undermined more than a decade of denial from medical professionals of their complicity in post-9/11 interrogations, the APA’s 173-member council of representatives consented almost unanimously to ban its thousands of psychologists from being involved in Bush-era tactics of torture as well as present-day non-coercive techniques.

Concerns among reformers about growing opposition from military psychologists turned to joy and relief as only council member, Guantánamo Bay and Abu Ghraib military psychologist Larry James, dissented against a detailed resolution prepared by longstanding critics in the Coalition for an Ethical Psychology.

“This is an extraordinary victory because these prohibitions are clear, they’re implementable, and people will be held accountable,” council member Steven Reisner, a leader of the group’s reform coalition, said.

The vote, at the annual convention of the group, which counts more than 130,000 medical professionals among its members, will turn the APA “from leading us into the dark side to leading us out of the dark side”, he said.

Although the prohibition applies exclusively to interrogations carried out in the name of national security abroad and at “black sites”, Reisner said reformers are hoping to expand the prohibitions to prevent psychologists from abetting “domestic cruelty” in the US justice system. “We have to consider that in the future,” he said.

Indeed, reformers stressed that the vote in Toronto by no means marked the end of a nine-year campaign to restore the APA’s “moral compass”. They were long belittled and suppressed by the leadership of the organization, which retains enormous influence in setting standards of psychological practice and ethics in the US and elsewhere.

But last month, the reformers were vindicated by a scathing report from former US attorney David Hoffman, which found the group’s senior officials had adapted internal rules – and collaborated with the US military – to permit medical assistance in developing so-called “enhanced interrogation techniques”.

“We think there is something profoundly wrong with the way the organization functions,” said coalition member Stephen Soldz, describing a “general atmosphere of suppression and bullying” that prevailed until the report’s release. “No one in leadership ever spoke up against it. Not one board member or anyone in leadership over the past 10 years said, ‘This is not right.’”

The sense of unfinished business was personified by council member Jean Maria Arrigo, who first blew the whistle on the APA’s torture collusion and suffered the worst of the personal attacks and slurs as a result.

In accepting an award from a newly contrite leadership “as the finest possible role model for us in the profession of psychiatry”, Arrigo pronounced herself both “very touched” and “very wary that this is a public relations event meant to shut me up”.

Arrigo vented frustration about “having to spend 10 years of my life being a critic and a nuisance”, and insisted that the work of institutional reform had only just begun for a group she said had been “dedicated to looking the other way” and had spent too long “interlocked with the national security establishment”.

“We have to negotiate the issue between psychological ethics and national security. That’s the real work that we have to do.”