The editor of the Observer Roger Alton is leaving his post to be replaced by the paper's deputy editor John Mulholland, it has been announced.
Mr Mulholland has been deputy editor since 1998.
Industry analysts believe the move is the result of a power struggle with the Observer's sister paper the Guardian.
Mr Alton, 59, has held his job for almost a decade. This year the paper out-performed all other broadsheets.
In a statement which gave nothing away, Mr Alton said: "This is the right time for me now to be handing over to John."
Earlier in the year the paper won the Newspaper of the Year trophy at the British Press Awards.
Mr Alton introduced the Sunday newspaper's monthly Sport, Food, Music and Woman magazines, and lead the paper's move to the Berliner format.
He has also twice been named Editor of the Year.
Media pundit Stephen Glover, writing in the Independent, said Mr Alton's departure was a result of a power struggle with the Guardian editor, Alan Rusbridger, who resented The Observer's independence of thought and rising circulation figures.
Mr Glover wrote: "This is above all a Shakespearean tale of jealousy and power. If Mr Alton had not been so successful he might have survived."
Mr Alton said: "The Observer is in fantastic shape, editorially and commercially.
"I am absolutely thrilled at his appointment - he's a fabulous journalist and a dear friend I would trust with my life.
"John cares passionately about The Observer, and has a clear vision and ambition for its print and digital future. The paper is in very safe hands."
Liz Forgan, chair of The Scott Trust, owner of The Guardian and Observer, said: "We are very grateful to Roger for the passion and commitment he has brought to The Observer and The Guardian over the last 30 years.
"The award of Newspaper of the Year was a fitting tribute to an inspiring