He can now see the "finishing line" as he puts it, with his final speech in Parliament scheduled for next Wednesday and his resignation taking effect from April 14.
Key has not yet settled on what directorships he will accept in life after politics, which he came to in 2002 after a successful career abroad as a Merrill Lynch executive.
"I have started the process to assess what life after politics looks like by going through a whole bunch of things I knew we didn't want to do and that included I didn't want to live overseas, I didn't want to work 100 hours a week again."
He has had a couple of very attractive job offers including chairing an institution that would have required him to be based in London and which would have kept him out of New Zealand for five years.
"And I don't want to do that," he said.
"Having returned from being away for a long time, in that 15-year period other than the political role I played, we as a family have established a whole network of friends and relationships.
"I love New Zealand and I'm proud of what the Government achieved in the time that I led it and for me personally it just doesn't feel right heading off and doing something completely independent overseas."
He plans to do some international speaking engagements, some charity work and accept some directorships.
"But I want to be commercially focused and I can do those things in New Zealand.
"Once you establish you can see the sorts of things you might want to do and there'll be a range in there. While there'll be a bit of international speaking and a bit of international representation of organisations, realistically the bigger long term picture over the next 10 years is likely to involve me being on some corporate boards that interest me."
One role Key has accepted is to become patron and representative for Japanese billionaire, golf-loving and arts-mad philanthropist Haruhisa Handa.
Handa established ISPS Handa, a not-for-profit organisation that sponsors both professional and charity events, and the Handa Foundation charity.
"He is the leading world advocate for blind and disabled golf," says Key.
"He also has an orphanage and a big hospital in Cambodia so I'm going back to Cambodia in about three weeks to go and spend a few days around that.
"He does a lot in a range of charitable areas and I'm his patron for a couple of those charitable things and I represent him."
Key went to Adelaide and Perth for the Australian Open and to Queenstown for the New Zealand Open which ISPS Handa sponsored.
Handa is going to become the principal sponsor of football in New Zealand.
"He supports a lot of art and a lot of sport so I'm going to be involved in that as well."
Key found time to talk from Los Angeles where he was on his way from playing golf in August, Georgia, to attend a Handa-sponsored children's charity art exhibition and dinner event in Tokyo with his wife, Bronagh.
Handa spent a lot of time in New Zealand and Australia.
"He does all sorts of stuff. He does opera in front of the Opera House which is happening on March 24 in Sydney and he supports the national singing scholar, just a huge range of things. "
Key said he first wanted to get to know Handa when he heard he was sponsoring a lot of things in New Zealand.
"It was just interesting about why he was putting so much money into these events and I met him in Japan.
"Over the years I have met him a few times and when I was no longer Prime Minister, I literally got a phone call in Maui to say would I think about representing him a little bit."
On this visit to Tokyo, Key won't be calling in on Prime Minister Shinzo Abe to chew the fat over TPP, but said he would visit him at some point.
"He's great. I like him," said Key.
"All the Prime Ministers that I hung around with once I left were amazing and generous. They rang and wrote and they wanted me to come and see them and I will over time.
"But it's one of those things where you don't want to overstay your welcome and I'll be in Japan a bit so I'm definitely go and see him."
He has not yet seen former US president and golfing buddy Barack Obama but he was due to call him in the next couple of weeks. He has however had lunch in Australia with Prime Minister Malcolm Turnbull and breakfast with former Canadian Prime Minister Stephen Harper when he was in town recently.
He went to Munich in January to chair the International Democrat Union and he and Bronagh had a couple of big trips planned in the European summer.
"It has been busy. We've been travelling quite a lot and I suspect that will carry on."
It had taken some adjustment managing his own travel though, he said.
"I look after myself now which has been a remarkable experience, not to lose your passport, going through immigration."
In Los Angeles, Key agreed to be a surprise guest and speaker at a trade seminar yesterday organised by outgoing Consul-General Leon Grice.
Pakuranga MP Maurice Williamson is due to replace Grice as soon as he leaves Parliament.
So does Key ever have pangs of guilt for resigning and reducing National's chance of re-election?
He is not so sure National is less likely to win without him.
The public and private polling figures he had seen on Bill English suggested his personal ratings were strong.
"My sense of the country is it is just inevitable with politics; often they want continuity but they also want change. So with Bill they get continuity.
"Secondly in the event that there is a coalition deal that needs to be done, I suspect that for all parties it will be easier to do that coalition deal, if it requires New Zealand First, with Bill English than it would be with me."
In 2008 after leader Winston Peters had been involved in two separate donations scandals, Key ruled out working with New Zealand First on the issue of trust and the party failed to make it back to Parliament.
Key again ruled out working with New Zealand First before the 2011 election, at which the party was returned to Parliament, but Key had the numbers anyway.
Key said it was not a matter of having a toxic relationship with Peters.
"In a different world him and I probably could have got on extremely well," he said. "I've been at parliamentary functions and I've taken him away on international trips. As everybody knows who knows Winston, he can be thoroughly personable.
"But he certainly had a different worldview to me."
Key said he had stayed below the radar for the past few months to give 100 per cent support to English.
"Inevitably I can only cause distraction or inadvertently become a story.
"That would be immensely unhelpful to the Government. But also the focus has to be on Bill English as Prime Minister and the country has to get to know him.
"I owe it to him to give him maximum space and freedom for the country to learn to know how good he is and if I'm there I just clutter that space."
Key said he would do a few interviews next week but he was then going to stay below the radar at least until the election in September.
"I desperately want Bill to be the Prime Minister and be a successful one so I need to be the most committed buying into that process.
"But I think he is going to win, that's my own view."
He gives English top marks. English looked as though he was enjoying the job, he was not letting it get on top of him and he was making hard decisions.
"It is always tough in election year and you never want to let that worry you. You've just got to get on and do your job and in the end, what will be will be."
