Twenty years after Tony Blair swept to power with a landslide vote, Lord Darling of Roulanish appeared to rule out the prospect of a Labour victory.
He said: "It's important we get the best possible result for the country, that means having a sensible sizeable opposition that can actually make a difference.”
Asked if he endorsed Mr Corbyn, the former MP and chancellor said: "He is the leader, he is the leader right up to the general election.
"My view is we need to get on, we're fighting a general election campaign, you know leaders come and go."
He added: "There's no question he's the leader, it's for him to convince people in the next six weeks and voters will make of it what they will."
Lord Darling was speaking while campaigning in Edinburgh South - the seat held by Labour's one remaining Scottish MP, Ian Murray.
The former chancellor, who also headed the campaign to keep Scotland in the UK in 2014, also urged voters to reject the SNP’s bid for a second independence referendum.
He said it was important to get "people like Ian returned at the next election so we've got decent people arguing against an ever more extreme, bleak view of what might happen”.
He argued that politics had "skewed to the right" under the Conservatives, leaving so-called Middle Britain unrepresented.
He also warned against the election being hijacked by “extreme people with a bleak, narrow view of our country’s future”, echoing comments made by Theresa May on a Scottish campaign visit at the weekend.
He claimed voting Labour would prevent the country’s future being hijacked by Tory Brexiteers and send a message to Ms Sturgeon that voters north of the border do not want another “divisive independence referendum”.
He said: “We can’t let this election be hijacked by a group of extreme people with a bleak, narrow view of our country’s future.
“People don’t have to choose between Brexit nationalism and Scottish nationalism.
"We decided three years ago very clearly that we wanted to stay in the United Kingdom. We were told it was a once-in-a-generation choice then, and many people believed that was the case. We don't want to reopen that.”
On a flying visit to Deeside on Saturday, the Prime Minister said that building a more secure and united nation meant “taking action against the extremists who would divide us and standing up against the separatists who want to break up our country”.
Nicola Sturgeon, campaigning in Aberdeenshire, said: "Alistair Darling could be talking about health and education or the economy, instead he's choosing to talk about independence while I'm here in the north-east talking about childcare.
"So perhaps Alistair Darling should direct his message more at himself and his Labour colleagues than me.
"The fact of the matter is that Labour has got very little positive to say in this election.”