The finding was presented at an worldwide AIDS Society Conference in France on Tuesday.
During the course of the study, participant couples reported nearly 17 thousand acts of anal-intercourse without a condom, none of which resulted in HIV transmission.
This "is the first study to show that these results apply in both high- and middle-income countries", Grulich said.
"The evidence is now clear that a person with undetectable viral load will not transmit the virus", he said.When one is undetectable, it's virtually impossible to transmit the virus. It further corroborated the findings of the previous PARTNER study, which also showed no HIV transmissions in mixed-status relationships where the virus is suppressed.
Dr Anthony Fauci, director of the US National Institute for Allergies and Infectious Diseases, said: "Scientists never like to use the word "Never" of a possible risk, but I think in this case we can say that the risk of transmission from an HIV-positive person who takes treatment and has an undetectable viral load may be so low as to be unmeasurable, and that's equivalent to saying they are uninfectious".
HIV positive gay men who are being successfully treated will not pass on the virus to their partners, research has found.
From 2012 to 2016, the study regularly checked in with 358 serodiscordant gay male couples (where one has HIV and the other does not) from Thailand, Brazil and Australia.
An additional 5,000 condomless sex acts took place between a partner with an undetectable viral load and a partner who was taking PrEP.
During the study, each couple had to report their sexual activities on their arrival at the clinic that conducted the study, and the couples were also tested to see is any new infections have been happening. And, according to Opposites Attract, that means the risk of transmission becomes negligible.
"It's a form of safe sex. they're not going to transmit HIV", he said. "The Evandro Chagas Clinical Research Institute is proud to be a part of this very important endeavour".
Together, the findings report not one single case of HIV transmission in almost 40,000 acts of condomless sex where the HIV-positive partner is on effective, HIV-supressing treatment.
"The Opposites Attract Study is ground-breaking Australian research".
"For many years. people with HIV have felt stigma in different ways and have been viewed by doctors or other community members as potential passers-on of something which is quite serious", he told the ABC.