Sir Keir has been criticised for his overly cautious approach to the Israel-Gaza conflict and mirroring the Conservative policy on immigration.
"I want to see our country change for the better and I don't think there's a strong enough offer being made," Mr Corbyn told 7.30.
"He was elected on the basis of supporting the policies that we'd fought the last two general elections on and then to sort of disappear from those policies is not a very good idea."
Mr Corbyn is now running as an independent in the North London constituency of Islington North.
"I'll be delighted to see the end of the Tory government," he said.
"I'll be delighted that there's been a change and hopefully I'll be in that parliament. If that government does good things, fine, I'll support them.
"But if they don't end child poverty, I'll be on their backs."
While Mr Corbyn was critical, advocates for the Labour leader say he is a much more complicated and aspirational figure.
His biographer and former senior Labour advisor Tom Baldwin has documented the Labour leader's unorthodox journey towards Number 10 Downing Street.
"Most are complicated but most politicians aren't really allowed to be complicated," Baldwin told 7.30.
"He's the first Labour leader to have the prefix 'sir' next to his name before he got the job but he's also probably the most working-class leader of the party for a generation."
Sir Keir often publicly discusses his working class roots and has frequently denounced snobbery in Britain's political discourse.
Baldwin believes Sir Keir's contempt for posh Britain, despite being a knight and an Oxford-educated former barrister, is genuine.
"He comes from a small village in Surrey, the sort of place you've never really heard of, unless you've lived there yourself," Baldwin said.
"His dad felt the sting of looking down at him because he worked in a factory. I think that's part of what drives Starmer now.
"He's the first Labour leader in my lifetime to talk a lot class and snobbery."
Despite involvement in the Labour movement as a teenager, a young Sir Keir never saw as a viable career.
"It was his parents who wanted him to become a lawyer," Baldwin said.
"It's quite a working-class thing. You don't go to university to study … you study for a trade and you can make some money as a lawyer.
"But when he got there … he didn't know the difference between a barrister and solicitor.
Birmingham was once a powerhouse industrial metropolis, but now the UK's second city is a shell of its former self as rubbish lines the streets, the lights stay off and children grow up below the poverty line.
"But as always, what he did is he worked harder than anyone else and found out he's better than them."
Sir Keir's knack for the legal profession led to a highly successful career as a human rights barrister, reaching the coveted Queen's Counsel status at just age 39.
But six years later the "lefty lawyer" made a career move that shocked his friends, becoming the director of public prosecutions.
"Becoming a top prosecutor was a weird thing to do if you're a lefty human rights lawyer, a lot of his friends were outraged," Baldwin told 7.30.
"[They told him,] 'We don't work with the police, we're against the police, we're against the state, we're against authority.' But at that stage I think he is beginning to move."
The position thrust Sir Keir into the UK's political milieu. The importance of his role meant he regularly dealt with the nation's attorney-general, former Tory MP Dominic Grieve.
Despite being a political rival of Sir Keir, Mr Grieve spoke glowingly of the former lawyer.
"I know it's been suggested he wasn't competent but that just isn't the case," Mr Grieve told 7.30.
"He had to carry out very substantial savings in his department to maintain its efficiency as well as taking correct decisions on prosecutorial matters.
One of Brexit's biggest supporters is likely to be voted in to parliament for the first time.
"I found him completely professional. I certainly never saw any political bias creep into his decision making. And he delivered."
The former Conservative minster also strongly refuted the accusations by former prime minister Boris Johnson that Sir Keir oversaw the failure to prosecute paedophile TV star Jimmy Savile.
"It wasn't a decision he made. Indeed, he wasn't even aware the decision had been made," Mr Grieve said.
"This particular story, blaming him for the failure to prosecute Savile is, I think, complete nonsense."
After years of crippling budget cuts, Sir Keir left the Crown Prosecutors office in 2014 and decided to try his hand at .
Baldwin said the Labour leader's early foray into the cut and thrust of the British political game did not excite Sir Keir and he considered quitting on more than one occasion.
"He doesn't like , he doesn't particularly want to engage in the transaction or dirty stuff. He'll do it because it's necessary," Baldwin said.
"The frustration he's had is, he thought he's going to come in, be part of the Labour government in 2015, and he's spent the last nine years in opposition. And what he says to me is, 'The last nine years have been the least productive in my life.'"
Sir Keir is seen by many political pundits as moving the Labour Party to the centre.
It's something the Greens are trying to capitalise on, with the party targeting historic Labour seats including in Bristol, which pollsters say will almost certainly be won by Greens councillor Carla Denyer.
"A lot of are disappointed and angry with the direction that the Conservatives have taken the country in, but they're also really feeling quite disappointed and uninspired by Keir Starmer's vision for the Labour Party," Ms Denyer told 7.30.
"I have a lot of voters saying to me on their doorsteps that they are struggling to see the difference between the Conservatives and Labour these days."
Baldwin though, says a shift to the centre and a boring, calculated approach to is what a struggling Britain and the Labour Party has been crying out for.
"There's only been three Labour leaders in the history of this country that have won elections and to win here in this environment, it's incredibly difficult," he said.
"Step-by-step he's taken the best route to get to the other side and he's absolutely determined.
"If you can start fixing some things, that will do more to restore faith in than pretending that you can fix everything."
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