Tony Blair and Gordon Brown have reached "a new understanding" which will see the chancellor take over as PM within two years, David Blunkett says.
The former cabinet minister hailed the understanding' saying "when they're divided, our opponents can divide us".
Whether Mr Brown took over in "a year or two years", it would be "a sensible process of combining the talents that we have", Mr Blunkett told the BBC.
Mr Blair has endorsed Mr Brown to succeed him as Labour leader.
Speaking about Mr Blair and Mr Brown's relationship, Mr Blunkett told the Sunday AM programme: "My sense is that there is a new understanding - yes.
"And it is good because anybody with any ounce of understanding of politics knows that when Tony Blair and Gordon Brown work together we are a winner. When they are divided, our opponents can divide us and it is as simple as that."
The Cabinet must be strong to ensure that the "very smart, very able" Tory leader David Cameron was not allowed to "occupy our territory", he added.
He said he hoped the debate over controversial education reform would be settled by the summer.
Mr Blair faces opposition from more than 90 backbenchers who fear poorer children will lose out under the plans.
But Mr Blunkett said there was a "real possibility" of a compromise and praised the prime minister for pushing ahead with the reform.
"If you take your foot off the accelerator, if you're not willing to look at new ways of providing incentives, providing support, providing momentum, you lose the plot," he said.
But before that, the party would need to unite to take on the Tories in the May local elections, Mr Blunkett added.
"I think we will have settled this [education reform] by the summer and we will take on the Conservatives and expose David Cameron, and goodness knows what will have happened to the Liberal Democrats by then," he said.
"But none of us ought to be in the least bit complacent because the May elections, including in London, are going to be extremely difficult for us," he added.
In a wide-ranging interview, Mr Blunkett also supported the government's attempts to push for 90-day detentions without charge for terror suspects, but said the move was not "fundamental" to security.
And he urged the government to carry on with plans for ID cards without compromise.
"You either have a proper, organised, verifiable, almost impossible to break system of identity which has the database, or you don't," he said.
His comments came as the independent reviewer of anti-terror laws said the cards would be of "limited value" against terror and would not have prevented the London attacks in July.
"I can't think of many terrorist incidents, in fact I can think of very few... that ID cards would have brought to an earlier end," Liberal Democrat peer Lord Carlile told GMTV.