Evening Standard editor Geordie Greig is leaving to edit the Mail on Sunday.
His deputy Sarah Sands is to be acting editor of the paper from 1 April.
Peter Wright, who has been editor of the MoS for 14 years, is to take up a new role as editor emeritus in charge of ethics and standards across Associated Newspapers.
Associated Newspapers editor in chief Paul Dacre said: "I'm delighted to welcome Geordie Greig from the Standard which he has edited with such Ã©lan.
"With his rich and diverse newspaper and magazine experience, I believe he will be a great success on the Mail on Sunday.
"I would also like to pay tribute to Peter Wright who has made a huge contribution to The Mail on Sunday – a paper he has edited with selflessness and huge journalistic skill over a period of great change.
"It is to the considerable benefit of Associated that he has decided to take on this important and challenging new role."
Greig was appointed editor of the Evening Standard three years ago, following the purchase of a 75 per cent state in it by Alexander Lebedev. He is understood to be a shareholder himself.
Before that he spent ten years as editor of monthly society magazine Tatler.
Lord Rothermere, Chairman of DMGT, said: 'I'm delighted to welcome Geordie Greig who has made such a success of the Standard and I believe will bring great strengths to The Mail on Sunday and its magazines, You and Live."
'I'd also like to express my gratitude to Peter for his distinguished and tireless editorship over so many years and to say how pleased I am that my company is retaining his wisdom and shrewdness.'