Speaking to NZ Herald Focus King said a percentage target was important to give people a clear direction to work towards, and that 20 per cent was "absolutely realistic".
He went further, saying New Zealand should aim for a suicide rate of zero.
"If everyone goes home tonight, sits down with their families and says 'We are going to have zero suicides in our family for the rest of this year. If anyone feels like they need to talk to someone I am here - who can I talk to?
"If we all individually target zero in our families, better support them, and have the information put in front of us that we can better support them then guess what, targeting zero is absolutely achievable."
King plans to keep working in the field of suicide prevention, he told Focus.
"I haven't quit doing what I'm doing - I'm just not going to waste any more time on a failed plan that has failed for the last 10 years and will not have my name associated with this current plan which is more of the same."
King told Newstalk ZB's Larry Williams this evening there had been no evaluation of the previous suicide prevention strategy so there was no way of knowing which services have worked and which haven't.
"We don't know what services are in place. We don't know how much money being spent."
King said the education, health, social development and justice ministries have no idea what each other are doing, so they are doubling up in some areas and short in other areas.
One of the first things the panel agreed on was that there should be a clear target for the country to move towards.
"We want the NZ public to take this seriously - we wanted to set a clear percentage goal on suicide prevention. So we decided to reduce suicide by 20 per cent over the next 10 years," he said.
But the draft proposal has removed that target and is extremely vague in its aspirations, King says.
In a letter to Ministry of Health director of mental health Dr John Crawshaw, King resigned from the panel saying he is growing "increasingly concerned" about the plan.
"The plan has buried all new ideas in such impenetrable language they are beyond recognition and unlikely to ever see the light of day.
"It is a strategy that is so broad in its effort to please everyone it will eventually collapse under the weight of public expectation. This will please no one except you and the politicians you serve," King wrote.
"It would be funny if people weren't dying," he added.
King says the draft plan ignores recommendations from the panel, continues to fund "failed experiments", is an almost word-for-word repeat of the last strategy - and will further isolate vulnerable Kiwis.
He went on to say statements made in the draft plan read like a political broadcast and were "so broad and vanilla they can mean everything and nothing at exactly the same time".
King also demanded to know why the 20 per cent reduction target had been removed from the plan, after everyone agreed it should be included in the plan.
"What happened to that [target]?" King asked. "Have we returned to the defeatist attitude that some degree of suicide is acceptable, inevitable or both?"
The Herald asked Health Minister Jonathan Coleman for comment, including why the 20 per cent target had been removed and why the previous strategy had not been evaluated.
Coleman did not address those questions, but said he would like to "acknowledge and thank Mr King".
"He's a passionate campaigner around this incredibly complex and sensitive area of health."
Every year around 540 people die by suicide in New Zealand.
King's resignation comes amid growing calls for an independent inquiry into the state of New Zealand's mental health sector.
Crawshaw said King emailed him earlier today outlining the reasoning behind his resignation.
"In my response to Mike, I'll be thanking him for his work, and also recognising the special connection he has with New Zealanders. His energy and drive will no doubt be ongoing as we all continue the work to reduce suicide," Crawshaw told the Herald.
The ministry has been consulting widely with the public and those involved in suicide prevention since the draft strategy was released last month, Crawshaw said.
He did not respond to questions on the ignored plea of panellists to include a target of 20 per cent reduction in suicide in 10 years in the draft strategy.
"The draft strategy Mike refers to is setting out a vision of how we can work together to prevent suicide; it's the responsibility of all of us. No one person or organisation can prevent suicide; we all need to be involved from government agencies to employers, neighbours and families," Crawshaw said.
Prime Minister Bill English said he knew Mike King and was not surprised King had decided to leave the panel, putting it down to King's likely frustration with bureaucracy.
"If someone had said to me 'how do you think Mike King would go on a Ministry of Health panel?' I would have said 'I think both parties will struggle with that.' That's because he has quite a different style and he's got his place, it's very effective in the way he does it. And it probably doesn't suit him sitting around in meetings talking about generalities."
English said King was probably appointed because it was thought he would have a constructive contribution "and I'm sure he's made a constructive contribution."
"I wouldn't criticise him at all for deciding he didn't want to continue with that process."
"Mike has been a very committed, highly motivated anti-suicide campaigner and he has a particular style and way in which he does that. I'm not surprised at all that he finds the Ministry of Health way of going about things not necessarily to his liking."
He said he was not surprised there were differences of opinion in an area such as suicide reduction. King did valuable work and "I'm sure he's saved lives with the work that he does.
"So they should take some notice of what he says."
The Greens health spokeswoman MP Julie Anne Genter said King had done "his utmost" to put this issue at the forefront of public and Government attention.
"For him to step away from this shows the utter frustration over the lack of forthcoming action on suicide and a Government missing in action on mental health."
She called for an urgent full inquiry "to get to the bottom of how future interventions can be the most effective."
Labour deputy leader Jacinda Ardern said King's resignation should be a "major red flag" for the Government.
"Mental health is reaching crisis point in New Zealand after years of National's $1.7 billion worth of cuts to health.
"It's clear the Government's approach is, sadly, now driving away some of the people who can do important work in this area.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.
