Peter Wallis will edit the weekday paper and Alison Phillips will oversee the Saturday and Sunday editions. Both are internal appointments.
They replace the Daily Mirror's Richard Wallace and Sunday Mirror's Tina Weaver, who were both sacked last month as part of Trinity Mirror's decision to merge both papers to a seven-day title, similar to Rupert Murdoch's move for The Sun.
The National Union of Journalists (NUJ) slammed the "brutal axing" of Wallace and Weaver, and said that the merger was a sign Trinity Mirror is a "company in crisis".
Peter Wallis started his 25-year journalism career at The Sun, but joined the Daily Mirror in 1997 as launch editor for the Saturday magazine.
Alison Phillips joined the Daily Mirror in 2001 as features editor, before becoming associate editor eight years ago. She previously worked for the Sunday People and Sunday People Magazine.
Lloyd Embley, the former editor of The People who is now overall editor for the Daily Mirror and Sunday Mirror, said: "These two positions are absolutely key to the seamless introduction of a seven-day operation at the Daily Mirror and Sunday Mirror.
"Peter and Alison are superbly talented journalists whose creativity, drive and instinct are exactly what we need.
"I worked with them both at the Daily Mirror for many years before editing The People and I know that we will make a dynamic team. These are richly-rewarded promotions for two of the finest journalists I know."