The findings are part of a comprehensive study undertaken by the Australian Bureau of Statistics as a 15-year first and aimed at understanding the impact of mental ill-health.
Australians aged 16 to 85 were surveyed and for the first time, the research gathered data from people on their lived experiences with suicide, self harm and binge eating.
It found almost two-in-five had been close to someone who had died by or attempted suicide.
In 2020/21 specifically, one-in-five people experienced a mental health disorder, with anxiety most common.
Deputy Chief Medical Officer for Mental Health Ruth Vine says the survey would hopefully help show people they are not alone and can seek help.
"It reinforces that ... many of us will know a person who has struggled and who has recovered and even grown in some ways through that experience," she told reporters on Friday.
More than one-in-five people rated their weight or shape as very important to how they thought about themselves as a person and one-in-20 had experienced binge eating.
"We know social media is both a good ... but also at times a harm if people who are vulnerable are accessing social media that might be focusing on body image," Dr Vine said.
The study found nearly 40 per cent of 16- to 24-year-olds experienced mental ill-health in 2020/21.
Young women were more likely to report experiencing a disorder, with almost half saying they had.
The National Mental Health Commission says the findings are deeply worrying.
"The commission is very concerned that the situation for young people appears, in fact, to be deteriorating," chair Lucy Brogden said in a statement.
"The commission is continuing its work with experts to deepen its understanding of what is causing this disturbing trend and to identify ways in which it can be addressed and reversed."
Nearly 45 per cent of people in the LGBTQI community experienced anxiety and three in 10 reported an experience with affective disorder such as depression.
The data highlights areas that require immediate action and improvement, Mrs Brogden said.
"Australians would have hoped to see an improvement in outcomes for those experiencing psychological distress and who have a diagnosis of mental illness. That is not the case," she said.
"More needs to be done in prevention, early intervention, the social determinants of good health and wellbeing and treatment."
Harmful alcohol use was more common among men, who were also more than twice as likely as women to have had a substance use disorder.
The study also looked at support services and whether they are making a difference.
Some 3.4 million Australians had at least one mental health consultation in 2020/21 and general practitioners were the most commonly consulted.
More than 24 per cent of people 16 to 34 saw someone about their mental wellbeing.
This compares with 16.8 per cent of 35 to 64 year olds and 7.5 per cent of over-65s.
Women were more likely to seek help and more than half all females with a mental disorder reported seeing a health professional compared with 37 per cent of all males.
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