Andy Burnham has pledged to work "in lockstep" with Welsh Labour to reverse its electoral decline, urging the party to "take stock" following its defeat at the Senedd elections.
The Prime Minister said he would avoid "creating problems" or "going against" the aims of Welsh leader Ken Skates, but warned the party must "listen" after losing to Plaid Cymru.
Labour had dominated Welsh politics for a century, yet went from holding power in Cardiff Bay to a distant third place behind Reform UK in May's polls.
Pledge to Rebuild
Speaking at the party's Welsh conference on Saturday, the Prime Minister said: "So, the next mission, of course, is to get the Everton-supporting leader of Welsh Labour as first minister of this great nation, and Ken, you and I are absolutely in lockstep on that mission."
He added: "So, for the first time in its history, Labour is not leading the Welsh government, and that's a hard thing for us all to have to accept.
"But, accept it we will, and come back stronger, and we will come back together with a vision for a stronger Wales within a fairer United Kingdom, and that's what I'm trying to leave with you as your Prime Minister."
Call for Change
Mr Burnham, who was still mayor of Greater Manchester when the elections took place, said: "You can't look away. You have to listen, take stock and commit to doing things differently. I'm always one for saying let's do politics differently.
"It doesn't connect with people as much as it should and I'm taking the way I approached being mayor of Greater Manchester into my work as Prime Minister.
"Let's be place first before we're party first, because at the end of the day, that is what people expect."
In keeping with his wider devolution agenda, the Prime Minister said the party must work towards a "reindustrialised nation" of Wales with "revitalised high streets and empowered communities, good jobs, evenly spread all over".
"A generation of Welsh workers created wealth that reached far beyond the places that they called home. But those industries declined, when there was money to be made elsewhere," he said.
"They were forgotten and that is something that has never left me. And that's what I'm determined to change as Prime Minister."
Review Findings
Arguing that devolution should also be pushed out into the Welsh regions instead of stopping at the Senedd, he said that "together we can make the next three about giving every region, every town and every community in Wales that voice too".
The review into Labour's May election defeat has been carried out by Public First, with findings set to be presented at the conference by leading academic Professor Anand Menon.
Mr Skates, who replaced former Welsh leader Baroness Eluned Morgan after she was unseated in May's polls, said: "The Senedd elections were a pivotal point for Welsh Labour.
"The results were catastrophic for the party, that was clear for all to see. But the reasons for our losses, and there were a multitude of reasons, needed a dispassionate assessment.
"Welsh Labour commissioned this independent review because we needed an honest account of why we lost and what must change.
"Its findings are difficult and we take them seriously.
"People felt that we had stopped listening, public services were not improving quickly enough and we had taken their support for granted.
"Our task is to earn trust again. We will listen carefully, develop a clear offer for Wales and demonstrate through our actions that we have learned."
