Martin Newland has resigned as editor of The Daily Telegraph, the newspaper has confirmed.
Martin Newland leaves the newspaper at the end of the month
Mr Newland, 44, was appointed in 2003, before current owners the Barclay brothers took over last year.
The BBC's Nick Higham said this had left him in "limbo", as it had been impossible to make any "major strategic decisions about the paper".
The Telegraph had been losing sales to rivals which had ditched the broadsheet format, he added.
'Could not continue'
Mr Newland will leave at the end of the month.
His departure follows the recent appointment of John Bryant as editor-in-chief of the Telegraph Group.
A Telegraph source said: "Martin felt that he could not continue in his position since the appointment of John Bryant as editor-in-chief."
Mr Newland said editing the paper had been "a privilege", adding: "It has been a marvellous experience working with so many great journalists and building the newspaper's reputation as the UK's market leader."
He thanked Sir David and Sir Frederick Barclay and Aidan Barclay for their "kindness and good wishes".
Telegraph Group chief executive Murdoch MacLennan said: "Martin Newland has guided the Daily Telegraph with distinction through a difficult period, especially during the sale of the company by Lord Black.
"He has attracted a team of brilliant writers, pioneered the new business and sports sections and overseen the re-design and modernisation of the newspaper."
The Daily Telegraph is still only available in broadsheet format
Mr Newland was thought to be opposed to introducing a tabloid version of the paper, which The Times and The Independent have already done.
The Telegraph's other "quality" rival, The Guardian, has moved to a "Berliner" format, slightly bigger than tabloid size.
Before becoming Telegraph editor, Mr Newland edited Canada's The Morning Post.
Prior to that he was previously home editor, news editor and a reporter for The Daily Telegraph.
Meanwhile, former Telegraph owner Conrad Black has denied charges of 11 counts of fraud in the US, linked to a $2.1bn (£1.2bn) sale of hundreds of Canadian newspapers.
US prosecutors say he and three other accused executives fraudulently diverted almost $84m from his media empire, Hollinger International.
An arrest warrant has been issued for the former Telegraph owner, who bought the paper in 1985, but sold it a year ago.
Lord Black was already facing a civil case brought by US regulators.