People currently get antiretroviral therapy only when their white blood cell levels drop.
But a US-led study has now been cut short as early treatment was so beneficial for patients.
The United Nations Aids agency has called for everyone to get immediate access to the drugs.
Around 35 million people are living with HIV and more than 2 million start antiretroviral therapy each year.
The discovery of drugs to attack the virus has profoundly changed the way the disease is treated.
But there has been fierce debate about when treatment should start.
World Health Organization guidelines say treatment should start when there are fewer than 500 white blood cells in every cubic millimetre of blood.
The trial on 4,685 people in 35 countries, organised by the US National Institutes of Health, compared this approach with immediate treatment.
The trial started in 2011 and was due to run until the end of 2016.
But an interim analysis of the data showed that cases of Aids, deaths and complications, such as kidney or liver disease, had already been halved by early treatment.
All patients on the trial are now being offered antiretroviral drugs.
The director of NIH's National Institute of Allergy and Infectious Diseases, Anthony Fauci, said: "We now have clear-cut proof that it is of significantly greater health benefit to an HIV-infected person to start antiretroviral therapy sooner rather than later.
"Moreover, early therapy conveys a double benefit, not only improving the health of individuals but at the same time, by lowering their viral load, reducing the risk they will transmit HIV to others.
"These findings have global implications for the treatment of HIV."
Michel Sidibe, executive director of at UNAids, argued: "Every person living with HIV should have immediate access to life-saving antiretroviral therapy.
"Delaying access to HIV treatment under any pretext is denying the right to health."
Dr Steve Taylor, the lead HIV Consultant at the Birmingham Heartlands HIV Service, told the BBC the trial was hugely important.
"Not least that they will they will change the way HIV treatment is prescribed in the UK and around the world.
"Based on this study, people will be able to access treatment much earlier than currently, which is good for their own health and will reduce HIV transmission."
Deborah Gold, chief executive of the National Aids Trust, said: "These exciting results should dramatically change the approach to treatment for people living with HIV, both in the UK and internationally."

Older People's Commissioner for Wales Sarah Rochira will call on pensioners and their friends and families to hear their experiences of residential care.
The evidence will be used to develop recommendations for care providers and public bodies.
It is part of Ms Rochira's review into the quality of life and care of older people in residential care in Wales.
She said she would highlight good care but also show the impact of poor care upon older people.
"The voices of older people, as well as those who care for and care about them, are at the heart of my work as commissioner, which is why I want to hear about their experiences of residential care," she said.
"I have travelled extensively across Wales, meeting with many older people living in residential care, and have seen for myself the positive impact that high quality care can have on people's lives.
"However, I have also received an increasing amount of correspondence in the past year about the quality of life and care of older people living in residential care and I have spoken publicly about what I consider to be unacceptable variations across Wales."
The commissioner will be reviewing whether older people living in residential care have a good quality of life by looking at factors such as physical and psychological health, social relationships and the care home environment.
Her team will also speak to care providers, social care staff and public bodies.
"By giving a voice to older people and their families, my review and recommendations will ensure that those who are accountable for and run our services understand the day-to-day realities of living in residential care in Wales and the action required to deliver the change needed to ensure that that older people living in residential care have the best quality of life," she said.
The chair of Care Forum Wales, Mario Kreft, said his group was dedicated to developing and promoting best practice in social care and it supported the overall aims of the review.
"Our disappointment however - which will be shared by many providers - is that the commissioner has not included a provider expert on the main advisory panel," he said.
"As far as we can see no-one who has lived in, worked in, managed or owned a care home is represented on the panel.
"In our view, this misses the opportunity for partnership working and to engage the sector fully into the advisory panel."
HIV drugs should be given at the moment of diagnosis, according to a major trial that could change the way millions of people are treated.
[NEXT_CONCEPT]
A review team looking at the quality of life of older people is to swoop unannounced on 100 care homes.