There is "zero chance" of a successful coup against Jeremy Corbyn, Labour's new deputy leader said - despite conceding significant policy differences with him on key issues.
Tom Watson said the left-winger was putting together a "broad based" shadow cabinet and urged moderate colleagues to respect the "huge mandate" provided by his convincing leadership contest win.
But he accepted there were crucial areas - such as the new leader's opposition to the renewal of the Trident nuclear deterrent and his approach to Nato - where compromise would have to be sought.
Mr Corbyn was declared Ed Miliband's successor on Saturday on the back of a surge of support from activists that saw him attract a massive 59.5% of votes - topping the ballot among party members as well as trade unionists and new supporters.
The immediate resignations of a string of senior figures who declared themselves unable to serve in his top team swiftly underlined the task he faced uniting the party behind his anti-war and anti-austerity platform.
Senior party veterans such as Peter Mandelson and David Blunkett were among those warning that the party risked becoming unelectable without action to temper the new leader's radical mandate.
Mr Watson - appearing on BBC1's Andrew Marr Show in place of the leader, who pulled out to concentrate on shaping his new team - said he understood the concerns of moderate colleagues about the seismic political shift.
"He wants to build a broad-based party, he wants a front bench that represents all the talents and all the views," he said.
"So I say to colleagues: watch this space, respect the mandate he has been given from our members, try to unify and let's try and get an exciting programme for 2020.
Asked about reports of behind-the-scenes moves to oust Mr Corbyn, he insisted: "There is zero chance of that happening; Labour Party members will not accept that."
In a signal of the potentially divisive battles to come Mr Watson - seen as a crucial linchpin in securing party unity - accepted that he and many other MPs backed the renewal of Trident.
"There are different views. Nobody wants to live in a nuclear world but it's how you disarm," he said.
"I think the deterrent has kept the peace in the world for half a century and I hope we can have that debate in the party".
He claimed there was no "massive disagreement" on Nato membership - but conceded he didn't know "precisely what Jeremy's position" was and hoped to "convince him of the merits".
"What I have read in the papers is that he actually understands that Nato needs to exist, he respects the views of many party MPs and members on this but he wants to make sure it doesn't expand eastwards.
"These things have got to be worked out."
"I aim to convince him of the merits of Nato. It was created by one of Labour's greatest ever foreign secretaries, Ernest Bevin, because his generation came through the Second World War and wanted to keep the peace."