The former Labour leader will be part of a commission made up of voices from “different Labour traditions” aimed at taking a “meaningful look” at why the party has lost four elections in a row.
Jeremy Corbyn has faced criticism for claiming Labour “won the argument” and writing only a generic letter of thanks to former MPs who lost their seats rather than apologising personally.
Yet the commissioners behind the independent review said it was wrong to blame only Mr Corbyn – or the position on Brexit – for Labour’s heaviest general election loss since 1935.
As well as Mr Miliband, who led the party to its 2015 defeat, former shadow education secretary Lucy Powell and Birmingham Ladywood MP Shabana Mahmood will spearhead the review on behalf of the Labour Together group.
Other confirmed commissioners include Jo Platt, a former MP for Leigh – one of the lost seats from Labour’s heartlands in Greater Manchester – Sienna Rodgers, editor of the LabourList website, and James Meadway, a former economic adviser to shadow chancellor John McDonnell.
The review will interview all 59 MPs who lost their seats during the crumbling of Labour’s “red wall” of constituencies in the north, the Midlands and Wales.
Labour Together describes itself as a “network for activists from all traditions of the Labour movement”. A trade union representative, as well as a local organiser, is also expected to join the panel.
“We have lost the last four elections and we all have to accept that our offers to the country have been insufficient,” said Ms Powell, the MP for Manchester Central. “We should have taken the time to understand our losses previously.
“It’s now profoundly important for the future of our party and country that we take a real and meaningful look at why we have fallen short.
“This inquiry gives us the opportunity to listen to members, candidates and the public and I hope our whole movement takes it in the spirit it is offered and takes part.”
The commission, according to a spokesman, aims to “raise above the factional infighting which has coloured much of Labour politics for the last four years”.
It hopes to capitalise on the “millions of conversations” voters had with Labour campaigners in a bid to come up with a plan for Labour’s return to Downing Street.
The party last won an election in 2005 under the leadership of Tony Blair.
The former Labour leader of 13 years gave a scathing speech last week, telling an audience in London that the “takeover of the Labour Party by the far-left” had “turned it into a glorified protest movement, with cult trimmings, utterly incapable of being a credible government”.
Laura Pidcock, a close ally of Mr Corbyn, caused a stir on Sunday by suggesting Mr Blair was still to blame for Labour’s crushing 2019 electoral defeat. She said the former prime minister’s legacy “hangs around this party like a millstone”.