Orygen executive director and University of Melbourne professor Patrick McGorry will use Wednesday's speech to delve into the system's deterioration and its implications for 'ordinary people'.

Professor McGorry, a long-time supporter of the Border's Winter Solstice event, will also discuss prevention and possible solutions.

Professor McGorry said Victoria was once the state that invested the most in mental health services, per capita.

He said Victoria's mental health system had since become the "basket case of the country," covering a fraction of Victorians living with serious mental illness.

Professor McGorry said quality of care was variable, and people were flooding into emergency departments because the community-based care the state had promised to build, sustain and grow had "really just collapsed."

"People are getting absolutely second-class healthcare in probably the most important healthcare there is," he said.

"The optimistic side of it is now it's being understood and appreciated that this is a serious problem. Also, there are solutions.

"With the Royal Commission [into Victoria's Mental Health System] and the Productivity Commission [and its inquiry into mental health], there's a sense we might see more investment."

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He said the Productivity Commission's interim report, released late last month, reinforced that mental health care was being seriously underfunded.

The Royal Commission is expected to hand down its interim report by the end of this month.

Professor McGorry chairs the Royal Commission's expert advisory committee.

He said there was promise of a new dawn for mental health services.

"You get a sense big things could happen now and the whole system could be redesigned properly," he said.

"I feel very optimistic about it at the moment."

Asked why he chose to speak on Wednesday about "Victoria's mental breakdown, recovery and design", Professor McGorry said it was important the public understood how the system had come to be the way it was and where it could be headed.

He planned to describe the shift from an institutional model to the promise of a "modern, community-based mental health care" system and the ensuing "scandal" and "crisis".

"This [mental health] is one of the top three areas of non-communicable disease," Professor McGorry said.

He believed mental illness to be the most impactful on people's lives, as it often struck in the prime of their lives and if it didn't get better the effects spanned all of the productive years of adult life.

"Seventy-five per cent of mental illnesses appear before the age of 25," Professor McGorry said.

"If you want to change the course, there definitely needs to be a major focus on young people."

One in two Australians experience mental illness in their lifetimes.

Australia spends $18 billion a year on mental health, according to the Productivity Commission.

Yet, mental ill-health and suicide are estimated to have an economic impact of $51 billion a year.

"The very thing that hasn't been done is funding the mental health system to scale," Professor McGorry said.

"The under-funding is gross so people don't get effective care."

He urged people concerned about the mental health system to engage and get involved in discussions, because politicians could only do so much without a groundswell of public support for change.

"This is the last frontier we need to focus on," Professor McGorry said.

"We can transform the landscape of care."

Central Victorian services, collectives and individuals made submissions to the Royal Commission, with concerns ranging from funding to acknowledgement of the importance of carers.

The Violet Marshman Oration honours the late western Victorian nurse Violet Vines Marshman and her contribution to the health and wellbeing of people in rural and regional Australia.