Thelma Walker, who was MP for Colne Valley between 2017 and 2019, says her new party offers an alternative home for 'democratic socialists' who have lost faith in Labour under Keir Starmer's leadership.
The former headteacher left Labour last year and quickly joined the new Northern Independence Party (NIP) after "hitting it off" with its founder Philip Proudfoot on social media.
She has since been chosen to stand in the Hartlepool by-election for the democratic socialist political party, which says it want to make northern England an independent state under the name Northumbria.
The party will not be on the Hartlepool by-election ballot after they failed to register with the electoral commission in time, meaning Mrs Walker will stand as an independent.
But Labour officials fear she could still play a decisive role in deciding who wins the seat on May 6 by splitting the vote with its own candidate, former Stockton South MP Paul Williams.
A recent poll showed her to be third behind Dr Williams and Conservative candidate Jill Mortimer, a councillor in North Yorkshire, putting her ahead of the Liberal Democrats, Greens, and Reform UK.
Mrs Walker, an ally of former Shadow Chancellor John McDonnell while an MP, said her new party was 'light-hearted' in its approach and used a whippet as its logo.
She told The Yorkshire Post's political podcast, Pod's Own Country: "But actually, it's pride in our heritage. And it's OK for us to laugh at ourselves. Because we're proud of our northern heritage and our roots and our identity. And I think it's that banter that people have engaged with.
"But there's a very serious message about social justice and about addressing inequality and about that north-south divide. It's obviously hit us the hardest over austerity for the last nearly 11 years but decade after decade the North has been promised, with this leveling up agenda and this discussion about managed decline, but for me, it's been managed neglect."
Mrs Walker criticised the direction of Labour under Sir Keir and its decision to impose a candidate on Hartlepool without consulting locals. She said Labour activists had accused her of splitting the vote in the by-election, called after the resignation of Mike Hill, but insisted NIP was now the best choice for left-wing voters.
She said: "I don't know whether I'll win in Hartlepool, I'm working towards a win, I would love to win, I would love to represent the people in Hartlepool.
"But if it does nothing else, then [it will] get the message out from Northern people and people in Hartlepool, in particular, to say, we've had enough of this. I've talked about the crumbs from the Westminster table really, that it's always the leftovers that seem to come to the North, and promises that are often not fulfilled. And I think it's that taking control away from Westminster.
"So the important thing for me is getting that message out really, that I don't think what's happening here in Hartlepool is going to go away.
"I think we've now got members across the country who are joining up, many of whom are actually Northerners, who have ended up moving away from their home, to get employment to get those higher skilled jobs, because there often isn't that opportunity in the place where they were born.
"And so we've got this drain of our young people from places like Hartlepool, and actually in Colne Valley our own two sons, who are in London now, and went to London to get their particular jobs.
"That shouldn't be happening because northerners are proud of being born in the North, and they should have that opportunity to have affordable housing and to have skilled employment. And so that that's really the serious message."