ACT Minister for Health Meegan Fitzharris confirmed the event's promoter Cattleyard Promotions had given the green light for the trial on Thursday.

"The trial does not condone illicit drug use, however will provide an opportunity to encourage people who are considering using illicit drugs to modify their behaviour in ways that reduce risks of harm to their health," she said.

Festival-goers at the sold-out event at the University of Canberra will see a new tent in the crowd, where free pill testing will be run by the independent Safety Testing Advisory Service at Festivals and Events (STA-SAFE) consortium.

The trial already had the backing of the ACT government and the university as well as police and health authorities but negotiations with Cattleyard had gone down to the wire as the festival loomed.

Cattleyard had most recently given approval for the trial on the grounds it would be offered blanket indemnity should anything go wrong.

The consortium had offered the promoter a legal waiver only on issues related to pill testing.

It was unclear why Cattleyard had changed its mind late Thursday as repeated attempts to contact the promoter were unanswered.

Harm minimisation advocates have long pushed for pill testing at festivals, arguing it had been effective in protecting young people when implemented overseas.

A letter co-signed by a suite of health experts and advocates sent to Cattleyard this month said allowing the trial would "potentially save lives".

"Research shows that pill-testing helps young people avoid the dangers of unknown and contaminated drugs, and provides an opportunity for drugs to be disposed of before lives are put at risk," the letter said.

ACT Greens MLA Shane Rattenbury celebrated Thursday's news on social media.

"This is a fantastic outcome that will keep young lives safe," he tweeted.

The territory government first gave STA-SAFE permission to test drugs at the Spilt Milk festival at Canberra's Commonwealth Park in November last year but the trial was shelved just weeks out from the event.

While the promoter claimed it was a problem with paperwork, the local branch of the Liberal party was accused of "sabotaging" the trial by calling on their federal colleagues to intervene.

On Sunday, consortium volunteers at Groovin the Moo will also conduct a survey of drug users, allowing for data collection on a "largely invisible" consumer group, while an evaluation of the pilot will be conducted by an independent researcher.

Ms Fitzharris has previously assured punters police would not be waiting outside the pill testing tent to prosecute people testing their drugs.

Consortium members were also contacted for comment on Thursday.

- with Emily Baker.