The editors of the Daily Mirror and Sunday Mirror have been made redundant "with immediate effect" after the company announced it was moving to a seven-day operation.
Richard Wallace and Tina Weaver were told this morning they were losing their jobs and have been replaced Lloyd Embley who had been editing The People.
The move to a seven-day operation comes after tabloid rival The Sun launched a Sunday edition following the demise of the News of the World.
Critics described the move as "brutal" and a "shock", but Trinity Mirror said it was a "further step towards creating one of the most technologically advanced and operationally efficient newsrooms in Europe".
The company plans to appoint a weekday and a weekend editor to work under Mr Embley and a new editor for the People and said it will launch e-editions of its papers for tablet computers.
Mr Wallace was the Sunday Mirror's deputy editor until taking the top job at the Daily Mirror in 2004, having worked as a showbiz reporter at the paper previously. He replaced Piers Morgan at the helm of the tabloid when Mr Morgan was dismissed after publishing photographs - later shown to be fakes - which purported to show British soldiers abusing Iraqi prisoners.
Ms Weaver became editor at the Sunday Mirror in 2001 after working her way up as a reporter on the now defunct Today and the Daily Mirror.
Former Daily Mirror editor Roy Greenslade said the sacking of the pair came "as a shock to them and their staff".
Writing in his blog on the Guardian website, he said the decision was "a misguided move" by outgoing Trinity Mirror chief executive Sly Bailey, who is stepping down from her role at the end of the year.