Gen Kitchen, the new MP for Wellingborough, said she was “ecstatic” at the result, and the double by-election win for Labour shows people are “fed up” and want change.
The candidate said she cut short her honeymoon to begin campaigning when she was told former Conservative MP Peter Bone had been suspended from the Commons.
She was announced as the winner just over two hours after Labour also triumphed at Kingswood and she achieved the second largest swing from Tory to Labour at a by-election since the Second World War.
“I hope Damien (Egan, new Labour MP for Kingswood) is as ecstatic as I am, and I’m sure the Labour leadership will be as well,” she said.
“This shows that people are fed up, they want change, they want competency, they want pragmatism and they want politicians to under-promise and over-deliver, which is what I am hoping to do.
“It shows how much hard work we put in and the real positive message we were putting out. There is a real appetite for a fresh start and change.”
When asked whether she could replicate her win at the next general election, she said: “There’s a lot of try before you buy, a lot of people lending their votes.
“I have to make sure they buy again, so I will be out door-knocking, campaigning and delivering on our pledges.
“I will be working incredibly hard to secure their votes whenever the general election comes and I will be working really hard on our case work that we have picked up on at the doors.
“We have had so many people say they haven’t had a politician knock on their doors in the last 20 years. It means we have to make sure we deliver on the promises we have made.”
Reform Party
The Reform party finished third with 13 per cent of the vote, its best performance at a by-election, and candidate Ben Habib hailed it as “remarkable”.
Asked why people voted for him, he said: “People are absolutely fed up with the manner in which this country is being governed.”
On whether Reform is letting Labour leader Sir Keir Starmer into Number 10, he said: “The only reason Labour win, if Labour win, is because the Tory party is utterly useless.
“The Conservative Party is the problem and they need to go.”
The Conservative candidate, Helen Harrison, left quickly after the results were declared without commenting as the party’s vote plummeted from 32,277 at the last general election to just 7,408.
Her selection as candidate was controversial as she is the partner of Mr Bone, who received a six-week suspension from the Commons when an inquiry found he had subjected a staff member to bullying and sexual misconduct.
Prime Minister Rishi Sunak last month declined to say whether he would be campaigning for her.
Related: New Labour Kingswood MP says Conservatives have ‘sucked hope out of country’