"I think largely I could do with putting my skills into a new environment," he told Journalism.co.uk when we spoke to him more about the move.
In the Q&A below we hear more from Kelly on his move away from national newspapers and his reflections on the successes and changes for the Mirror and the digital content arena in recent years.
Q. Looking at the business side first. A couple of years ago you spoke about wanting to bring the revenues forward at the Mirror. Given the recent financial results would you say that has been achieved?
A. "Totally. It's been achieved by having better products in the market ... we haven't stood still, we've relaunched Mirror online, four or five times at least and I think the latest iteration is a quite superb website and we're seeing our engagement metrics going through the roof and the money is now following a passionate engaged audience.
"That's great news for people like newspaper groups who've got great content and great journalistic skillsets in engaging an audience which some other digital pure plays don't have.
"This website is getting much closer to being a great combination of journalistic skill plus technology and that's where the revenue is coming."
Q. Talking of the site redesign, what does the current design say about the future direction of the Mirror's journalism?
A. "Obviously this is for somebody else to take forward, but I think the site is now on a path to really establishing itself as a strong digital platform, rather than being a website of a newspaper.
"It's got its own audience, it's got its own content, so it's incredibly sophisticated in its technology but what I would say is that underneath all that and underpinning all of that is the same great quality journalism that has underpinned the success of the Mirror for more than 100 years and that is founded in being a paper that speaks in plain English to real people about things that they really care about.
"Those are eternal values and I think that's what we tried very hard to do in the design of the site, is to give some visual indications about the history and the heritage of the site but also not to let that history or heritage get in the way of establishing ourselves as a powerful digital platform."
Q. You're now moving on to other things, but what would you have said would be the top priorities for whoever steps into your role?
A. "I think it's always good after somebody's been in a particular role for a long time, like I have, it's good for whoever follows him to come in and try to have as fresher pair of eyes on it as possible, because like anything there are things that I haven't seen or directions I have spotted that somebody else with a new set of perspectives could come in and take up and run with it.
"But we're on the right path in the sense that it's all about engagement. It's not about raw traffic numbers, although they are obviously massively important. It's about big traffic with engaged audiences. And keeping true to the spirit of the Daily Mirror because after all that is the biggest advantage we've got out in the marketplace is that our brand means something real to people.
"I think we've set those values pretty much in stone and I think technology could get better, product could always keep improving, more journalism would be great but the framework is there for somebody to really take it forward."
Q. You have spoken before about an obsession with metrics, have you seen a shift in this attitude?
A. "100 per cent. I think the biggest shift has been from Google. It would smack of arrogance to say Google come to my way of thinking, but I think certainly the way search has evolved.
"I think search as an industry is in trouble because it's much more about recommendation now. It's about social media and about people recommending content to other people.
"I think when I was railing against SEO it was in the days when you could stuff URLs full of keywords and Google would think that was a good thing, now Google thinks that's a bad thing. So that's good.
"I think Google and the other search engines have come round to recognising that good journalism which is engaging journalism should be rewarded and not penalised online. That has definitely changed in the last two, three, four years."
Q. So how is the Mirror achieving the engagement you're speaking about?
A. "It's about understanding what we're great at and then using a combination of our great journalistic assets but also an obsession with data and an obsession with trying to introduce fantastic usable websites, mobile sites, and tablet properties for people to engage with wherever they are and also to put our content wherever people want to find it.
"So we're trying very hard to build our social media presence. MirrorFootball is a great example of that, I think we're close to 200,000 followers on Twitter now, it's got it's own style, it's different in the market place, it's funny, witty, it speaks in the same language as ordinary people.
"Those are points of differentiation that we're very keen to leverage in a marketplace where there's an awful lot of stuff that's all just the same. So we're trying to be different, we're trying to be clever in how we're different."
Q. When the Times paywall went up you said you were watching closely. What are your reflections on these models now?
A. "I think there are a lot of incredibly courageous experiments going on there and no one's completely nailed it and no one's got it completely wrong and I think the market is evolving.
Q. Finally, the proudest moment in your Mirror career?
A. "Probably the proudest thing actually thinking about it is putting together the Mirror online editorial team who are small in number but absolutely to a man terrific performers and I think without a shadow of a doubt the strongest editorial team head for head in Fleet Street.
"It's a very small team covering three major channels in news, MirrorFootball and 3am plus video, pictures, dwarfed by some of our competitors but pound for pound they punch well above their weight."