The former Labour minister confirmed she will stand for Commons Speaker as she praised outgoing Speaker John Bercow for his controversial style in the post. But Ms Harman, who had been previously suggested by some campaigners against a no deal Brexit as head of an interim cross-party government if Boris Johnson was ousted from Number 10 in the coming weeks, was confronted on her notorious anti-Brexit stance.
The former Labour deputy leader said the Speaker should not take sides politically but should allow Parliament to hold Government to account.
Ms Harman told BBC Radio 4's Today Programme: "It is the job of the Speaker to make sure that Parliament, by its majority, has its say, and I think that's what John Bercow has sought to do."
She added: "The Speaker doesn't vote, doesn't take sides in debates.
"But the Speaker is not neutral as between Parliament and the executive.
Brexit news: Harriet Harman, Commons Speaker candidate, grilled by Nick Robinson
The Speaker has to be on Parliament's side and stand up for Parliament
"The Speaker has to be on Parliament's side and stand up for Parliament.
"The Speaker cannot but allow Parliament to have its say on what it wants to do."
But BBC host Nick Robinson grilled the Speaker hopeful on her anti-Brexit sentiment and her credibility as a candidate.
He said: “You say it’s important to be neutral on certain aspects of the argument.
“Is it credible for you to present yourself as a neutral figure on the big divide of the day?
“Not between parties, but between Remainers and Leavers.
“You’ve talked less than a year ago about the devastating impact of Brexit.
“You accused the Government of having no credible plan and no viable solution.
“You said a no deal Brexit would be catastrophic. Won’t’ you get the votes of Remainers and simply not get the votes of Leavers?”
Ms Harman, who was a prominent Remain campaigner in the EU referendum, said she would be able to stand back from political issues if she became Speaker.
Lindsay Hoyle wife: Meet the woman behind potential Commons Speaker [INSIGHT]
John Bercow resigns: Who will be the next Speaker? [ANALYSIS]
Bridgen savages 'zombie Speaker' and reveals Boris' next move [VIDEO]
She replied: “The Speaker is chosen among MPs and all MPs are elected in a contested election where they put forward the views of their parties and their own political views.
“But once you offer yourself for election as Speaker, you’re making a promise that you will set that aside and that you will be neutral.
“So whoever goes forward to be Speaker will have to go through that transition where they say right, now I’m neutral.
“Unfortunately having been able to be Solicitor General where I had to step back and actually, in the public interest, not party interests.”
She added: "I think I would be a champion for Parliament.
"The relationship between the Parliament and the public is very difficult at the moment and I think a really confident, positive voice, speaking about the importance of Parliament with the public, is necessary at this time."