Defence members contemplating suicide were trapped in a "don't tell" culture where reaching out for help was regarded as "career ending".
The founder of Roses in the Ocean, Bronwen Edwards, told the Royal Commission into Defence and Veteran Suicide that a 2019 survey identified 65 per cent of defence members had admitted to suicidal thoughts.
"People in Defence are suffering with the impact of suicide at all levels," Ms Edwards told the commission.
"We were told there was a strong culture of don't tell, of stigma and don't be vulnerable within the ADF. Fear of career end or career pause is very real."
She set up Roses in the Ocean to lobby for better and more innovative programs for suicide prevention after her 43-year-old brother Mark Edwards killed himself in 2008.
Ms Edwards said while her brother, an ex RAAF fighter pilot combat instructor had spent the "happiest years of his life" in defence, a personal crisis after he left the forces led him to being treated with a "cocktail" of medications that "sent him on a spiral of eight years of suicidality".
"He was later advised that the treatment he received should never have been delivered... it really just caused a snowballing effect,' she said.
Ms Edwards said the treating doctor had been hauled before a medical tribunal after 11 people had died under his care.
"His hands were slapped, after admitting that my brother and others had literally been human guinea pigs, and tragically that person still practises today," she said.
She said 13 years after her brother's death there remained an urgent need to transform the approach to suicide prevention, and recognise "half of the people who die by suicide do not have a mental illness".
"We know that many people experiencing suicidality will not go anywhere near the mental health system because it doesn't resonate with them."
"Poor living circumstances, relationship breakdowns, financial concerns, drug and alcohol abuse bullying, lack of support... all sorts of things contribute to somebody actually getting to the point where they feel like killing themselves is the only option left."
The commission heard in 2019 the ADF had invited Roses in the Ocean to survey the attitudes among defence personnel for the establishment of suicide prevention peer support networks within defence - the Defence Lived Experience Framework Project.
Ms Edwards said while surveys revealed positive support for further help with suicide prevention inside defence, there were still "mixed messages about whether or not your job would be at risk if you ask for help".
"People have to be absolutely assured that by putting their hand up and saying 'I'm struggling with this or that' or 'I've got depression'," she said.
"They need to know that they can do that and just be treated normally and supported to stay in their role.
"I absolutely understand how complex it is. But a way has to be found."
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