He also congratulated John McDonnell, the shadow chancellor, for recruiting serious international economists to advise him on the future of the British economy.
Miliband insisted he would never be a “back-seat driver” as a former party leader and refused to predict whether Labour would do well under Corbyn, saying his own record showed “predictions aren’t my thing”.
His comments came a day after the shadow business secretary, Angela Eagle, refused to say that Corbyn and McDonnell were suitable for “the highest offices in the land”.
Appearing on BBC Radio 4’s Today programme on Monday, Miliband was asked whether his successor was suited to being prime minister.
He replied: “Of course. In the end that’s a decision for the electorate, as I discovered to my cost. That’s a decision the electorate has to make.”
Miliband added: “I believe that he wants a fairer country and, if you look at some of the people that John McDonnell has brought – Thomas Piketty, Joseph Stiglitz – international economists, they are the people actually arguing for this big question that our country faces, and this doesn’t go away.
“We’ve got a country divided, I believe, between the top 1% and everybody else – that is the new inequality.”
Asked whether Labour was stronger or weaker than when he was leader, he said: “I think it has a strength in depth in terms of our membership which we didn’t have before. Jeremy Corbyn has doubled our membership and I’ve seen that myself in my own constituency as a constituency MP – and I think this is quite important.
“I’m seeking to work out how do we use these new members so that we can do what we didn’t do fully under me, which is to become a community organisation that actually is a presence in communities up and down this country.”
He insisted he would not provide a running commentary on his successor.
“He’s going to argue it in his own way and he’s set out what he believes is his mandate for, which is anti-austerity, a different approach to foreign policy and participatory politics,” he said.
Miliband told interviewer James Naughtie that he was not going to be “a backseat driver” while Corbyn was in charge. Naughtie told him that, having “crashed the car”, that wouldn’t be appropriate anyway. “Thanks,” said Miliband.
Miliband was not asked about remarks reported in the media on Sunday, which suggest things have got worse under Corbyn.
There is still bitterness in parts of the parliamentary party that Miliband, shell-shocked by electoral defeat, did not stay on as caretaker leader to manage a postmortem, as well as oversee the election of his successor. His sudden departure, it is argued, left the party rudderless and vulnerable to an untested electoral system that allowed tens of thousands of people outside the party to vote for Corbyn.
Miliband was on the Today programme to discuss his call for legally binding targets to eradicate carbon emissions ahead of the climate change conference starting in Paris next week.
This article was written by Patrick Wintour Political editor, for theguardian.com on Monday 23rd November 2015 10.28 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010