Paul Feeney, chief executive of wealth management firm Quilter, is open about his past mental health issues.
Generally, though, he says, people in the City feel: "If I talk about it I'll lose my job."
"I've been in the City now for 30 years, I believe it's still now a really big stigma," he says.
It's a view mirrored in new research showing only 46% of financial services staff would be confident talking to managers about mental ill health.
The research, which has been shared exclusively with the BBC, was carried out by the Chartered Institute for Securities and Investment (CISI), the professional body for those working in wealth management and capital markets.
Of the 3,686 respondents, 23% said they were "unsure" and 31% said they were "not confident" talking to their managers if they felt they were suffering from stress, anxiety or depression.
Mr Feeney says he's not surprised by CISI's findings.
He told the BBC: "The City has been a macho culture, it's been a testosterone-fuelled culture, it's... basically Darwinian quite frankly, that's got to change.
"I think it's the last great taboo in the City, mental health, it's got to be called out."
Mr Feeney's own problems stemmed back to childhood - and he said it took him two decades to seek help.
However, he says a lot of problems in the City are "workload, work-related, stress, the belief that you've got to keep succeeding."
One respondent to the CISI survey who described themselves as a "senior in the business" and working in compliance, said they had been open about "situational stress".
They added: "The business is not good at helping me reduce my stress, however. My stress and anxiety stem from workload/pressure of work. I have taken time sick/come in late or left early."
Another said they had suffered "a number of breakdowns brought on by a wholly excessive workload".
"Until I collapsed in the office in front of a colleague and in pools of sweat having an anxiety attack, everyone seemed happy that the work was being done whilst I suffered," they added.
According to Simon Culhane, CISI chief executive: "The feedback in particular has shown that workload and working hours are root causes in respondents' experiences.
"The factors are controlled largely by the culture within a firm which is in itself determined by the leadership.
"If leaders have an enlightened approach to their own wellbeing as it relates to work stress, then this is an important example to set staff."
He said there were firms which were "leading the way" with their approaches to reducing the stigma about mental health.
Quilter's Paul Feeney says he wants to "try and make a difference here".
The company is backing wider efforts by employers and the City to tackle the problem, including the Time to Change Pledge, which urges firms to change how they think about mental health and better support staff.
It also runs its own internal initiative called "Thrive" which aims to "put these issues out in the open" by encouraging staff to talk openly about them.
Issues can range from post-traumatic stress disorder and bipolar to borderline personality disorder.
"Some of my most accomplished managers have come forward about the issues they're dealing with," he says.
However, Mr Feeney says: "This is not just philanthropic, it's hard business. A healthy workforce equals a wealthy company."