"If we bake mental wellbeing into the day-to-day workplace, it's simple - organisations will operate better, leaders will lead better, and individuals in the team will live and work better.
"I strongly believe that if we do a great job of this, we will see a reduction in accidents and injuries along with the other personal, organisational and societal benefits of a mentally well workforce."
ACC has invested in the platform through its $50 million Impact Fund. It won't say exactly how much it has invested but it is in the range of $2m to $15m.
Companies office records show it has taken an 11.45 per cent stake in Mentemia.
Meanwhile, ethical KiwiSaver provided Pathfinder has tipped in $800,000 and has a stake of 3.22 per cent.
They join existing investors Icehouse Ventures, which has 6.5 per cent, and Sir Stephen Tindall's investment fund K One W One, which has a 3 per cent share.
Sir John and his wife Fiorella Kirwan own 27.6 per cent of the company as does Clark's trustee company Sheaf.
ACC set up the Impact Fund last year with the twin aims of improving the health, safety and wellbeing of New Zealanders and providing a commercial investment return that helps keep levies low.
Impact Fund advisor George Adams said improving mental health and wellbeing could help bring down injury rates, speed recovery and reduce the cost in ACC claims.
"We encourage more companies to recognise the benefits of supporting the wellbeing of their workers, including better productivity and less time lost to injuries."
In 2019/20, ACC paid $65.5m for active work-related mental injury costs and $312m for mental injuries as a result of physical injuries in 2019/20.
Adams said mental health conditions, particularly depression, were a significant risk factor for higher rates of injury, slower rates of recovery and increased ACC claims costs.
Pathfinder CEO John Berry said its investment would make up around 1 per cent of its KiwiSaver funds.
He said KiwiSaver providers were increasingly moving into private equity investment because of the potential for delivering higher long-term returns.
"Social impact investments can deliver better outcomes for our planet and its people.
"We believe KiwiSaver investors are entitled to both higher returns and higher social impact," said Berry.