Video report by ITV News Correspondent Paul Davies
Mr Mercer did three tours in the British army in Afghanistan before becoming an MP and was appointed to the role in the new Veterans Affairs office by Prime Minister Boris Johnson in July.
In his first interview since taking on the role, the MP for Plymouth says he is bringing his personal experience of military life to the job in which one of the key remits is to tackle military mental health, including the rise in cases of post-traumatic stress disorder (PTSD) and suicide among veterans and serving military personnel.
He describes the current care available to veterans as "completely unacceptable".
An , working with veterans' groups, found more than 80 veterans and serving personnel took their own lives in 2018, while estimated suicide figures for this year stand at almost 50 - that is more than one a week.
The research compiled with the help of Veterans United Against Suicide last year found more than one third who took their own lives in 2018, and whose details are known, had suffered from PTSD - an anxiety disorder caused by very stressful, frightening or distressing events.
Mr Mercer told ITV News that he felt "enormous regret" for each one of the deaths and admitted successive governments had not done enough for veterans.
He said he was determined to provide those who have served the country with the "best mental health care in the world”.
"I'm not going to go out there and defend the way we have looked at this previously," he said, adding the ministry was working to bring a more coherent system that would track veterans through society once they leave active service - something that has not been done in the UK before.
Mr Mercer said he entered into the political arena with a view to delivering better provisions for military personnel suffering from mental health issues and said he was confident that within two years the Office for Veterans Affairs will deliver "a transformative experience" for service men and women, veterans and their families.
He said the country needed to "dial down the sympathy for those who have served" and should instead "put that energy into empathy" for veterans who "stumble across hard times".
"I've said this before in the House of Commons, the mental health challenge with repeated combat tours in theatre, whether it's in Iraq, Afghanistan, or wherever else, has completely ripped apart my circle of friends. So I have an intimate understanding of the issues.
"I am not going to pretend for a minute that I have all the answers, I don't think anybody has got all the answers.
"But I am determined to get the mental health care piece, whether it's in the veterans community, or the military or indeed in the NHS, to a place were we can offer those who have served in this country the best mental health care in the world.”
Mr Mercer said the current system was so fragmented that many veterans found it difficult to access the help they needed.
"This idea of telling your story in the first place is incredibly difficult, then having to re-tell it a number of times because every time you engage this service it's like you're starting from scratch, it's not an acceptable level of service to our veterans," he said.
"One of the crucial things we're doing is trying to establish what we call a single view of the veterans, so that anyone operating in this space can see whether this person has done, for example, the Hidden Wounds programme from Help for Heroes, and the journey that they've been on.
"Back when my cohort was going through the Afghan war, you'd have to go three-and-half, four hours for treatment - for a session of cognitive behavioural therapy that lasted an hour.
"People are not going to engage in that process, and I'm very clear about that. Using the data to establish proper case management for individuals is a huge part of what we're trying to do with the Office for Veterans Affairs."
Someone with PTSD often relives the traumatic event through nightmares and flashbacks, and may experience feelings of isolation, irritability and guilt.
Lance Corporal Dave Jukes took his own life in October 2018 behind the family's home in Birmingham.
"And really what he needed was one person who knew his story so he didn't have to keep living those traumas over and over, because that just made him worse."
Her message struck a chord with Mr Mercer, whose plans to co-ordinate existing services he hopes will be a major step towards realising his goal to make mental health care for Britain's military the best in the world.
What to do if you or someone you know needs help:
Combat Stress is available 24 hours a day on 0800 138 1619 for veterans and their families, 0800 323 444 for serving personnel and their families, via text on 07537 404719, or through .Veterans' charity