The Guardian is now the second most widely read English-language newspaper site in the world, say comScore figures released earlier this week, which show 42.6 million unique visitors to theguardian.com in September 2014.
This means the outlet has now leapfrogged the New York Times, which received 41.6 million uniques last month, but is still one step behind Mail Online, which had 55.8 million.
However, the comScore figures only record traffic from desktop computers and do not include mobile.
In a public lecture at the London School of Economics and Political Science (LSE) yesterday, Miller said the Guardian's success was underpinned by its commitment to open journalism.Open takes down the walls between journalists and readersAndrew Miller, Guardian Media Group
"Over 60,000 readers a day comment on our coverage," he said. "Today’s readers can correct, clarify and challenge the things our journalists write.
"Open takes down the walls between journalists and readers. It gives a richer picture of the world by collaborating with the new digital landscape, not fighting it."
Miller's lecture, titled Global News Media: The Next Horizon, touched on the various routes media organisations have taken to adapt to digital.
"Hiding your content, your single greatest asset, behind hard pay-walls and cutting it off from everyone but your most loyal readers misses the point," he said.
He added that the Guardian's commitment to openness stemmed not from "philanthropic reasons", but because it also made commercial sense to be open-source and interactive in order to become a "global media entity".
Miller said he was confident the Guardian would expand with "new editions and new bureaus", after the success of its Australian and US operations.The last thing we will cut to any depth is the journalismAndrew Miller, Guardian Media Group
Guardian Australia has almost two million web visitors a month, or 20 per cent of the market, he said, despite only launching in May last year.
Meanwhile, Guardian US receives 27 million monthly visitors.
A new office on the West Coast in the US was also in the works, he revealed, adding that a global media outlet not committed to the US "simply isn't a global media organisation at all".
But as the UK's commercial media outlets compete for online space with the license-fee funded BBC, Miller said the public service broadcaster could do more to support them.
He said a "new digital public space" could be created where the BBC's feeds would be open to UK's media outlets, who would be able to produce "more detailed storytelling" as a result.
And according to Miller, cutting costs at a news organisation only works if the aim is to reinvest, which the Guardian has done focusing on digital and hiring 10 digital journalism trainees last year.
"The last thing we will cut to any depth is the journalism," he said.
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