It found 48 per cent of Britons had experienced poor mental health in their job but only half of those had talked to their employer about it.
In a speech to launch the portal which went live on Tuesday, the duke said: "If you are a business owner, a team leader, a line manager, you work in HR, or just believe in supporting the wellbeing of your colleagues - Mental Health At Work can help".
A "STEP CHANGE" in workplace culture is needed in order to address mental health issues, a charity has said, after it revealed that nearly half of workers have experienced problems such as anxiety, low mood and stress. As many as 300,000 people lose their job each year due to a mental health problem.
But being a supportive manager can make a huge difference.
Speaking at the launch of the Mental Health at Work campaign in Bristol, England, in partnership with Heads Together and the Mind mental health charity, the Duke of Cambridge reveals he sometimes struggled after coming home from his job.
Workload along with hard relationships with line managers adversely affects the mental health of employees. Whether work environments contribute to the degradation of mental health or exacerbates conditions outside of the person's control, there's never been a more pertinent time for tools available to help those in work.
25%: This is the year-on-year increase of the number of days taken off work because of mental health issues.
Half of all employees are impacted by poor mental health.
It found that up to five million workers in Britain will experience a mental health issue this year. "The new online Mental Health at Work gateway will change that", Farmer added.
Employers throughout the United Kingdom were engaged in three rigorous rounds of user testing as the website was built. It brings together information, advice, resources and training that workplaces can use to improve wellbeing and give employees the mental health support they need.