The Government will commit to end the "modern-day injustice" of poor mental health at a global summit in London, after it emerged one in eight mental health staff left the NHS in a year.
Politicians, health experts and policy makers over the globe will meet in October to drive action on mental health, the Department of Health and Social Care (DHSC) said.
It follows Theresa May's pledge to ensure it is no longer treated as a secondary issue.
Health and Social Care secretary Matt Hancock (pictured) said: "For too long we have collectively failed to grasp the true magnitude of the problem.
"We owe it to everyone to put mental and physical health on an equal footing, to try and eradicate the apathy towards mental health once and for all.
"I urge policy makers and leaders to put mental health at the front of their minds."
The DHSC said it was transforming services with record amounts of funding, plans to increase the workforce and a special retention programme.
But Labour said its figures setting out how many mental health staff have left the NHS showed the Government was "woefully failing" to meet its commitment.
The figures, given to Labour MP Paula Sherriff, show 23,686 mental health staff left between June 2017 and the end of May, the equivalent of one in eight of the sector's workforce.
The shadow mental health minister said patients were being badly failed after the Government set out its ambition to increase the mental health workforce by 21,000.
Only 915 extra people have been introduced since the plan in July last year.
She said: "It is clear that NHS staff and patients alike are being badly failed under the Tories.
"Without drastic action, their targets will be left in tatters and it will be people living with mental illness who pay the price for this terrible failure."
Mental ill health is the leading cause of lost economic output, with an estimated cost of nearly 2.5 trillion US dollars (£1.9 trillion) annually across the globe, expected to increase to 6 trillion dollars (£4.6 trillion) by 2030.
A report endorsed by Mr Hancock, A Design For Life, says changes to the way cities are designed could add a £15 billion boost to the UK economy.
Introducing more communal seating, greenery, recreational areas and better street lighting could lead to increased workplace productivity, fewer absences and less reliance on the NHS, the report says.
It comes as Scottish Conservative leader Ruth Davidson emphatically ruled out a bid for Number 10 because she values her mental health and relationship too much.
In an interview with the Sunday Times she recalled being haunted by suicidal thoughts and depression, rolling up her sleeves to show the scars from the self-harm she experienced as a teenager.
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Kirsty O'Connor / PA Wire.