The former personal trainer, 45, won the West Yorkshire constituency with a majority of 323 votes, defying critics who said she was on course to lose after a bitter campaign and challenges from George Galloway and the Conservative candidate, Ryan Stephenson.
The “proud Yorkshirewoman” was born in Heckmondwike – within the boundary of the Batley and Spen seat – and her strong links to the area and high profile locally were hailed as part of the reason for her success.
Having attended university in Leeds and then Huddersfield, she began teaching at Bradford College while working as a wellbeing coach and fitness instructor.
In 2016 her sister Jo Cox, the former MP for Batley and Spen, was murdered by a right-wing extremist in the run-up to the EU referendum.
Soon after Ms Leadbeater began volunteering with the More in Common Batley and Spen group, part of The Jo Cox Foundation, which was established in the wake of her death to promote more cohesive communities both locally and nationally.
She then moved to work as an ambassador for the Jo Cox Foundation and was appointed MBE in the most recent New Year's Honours for her work in tackling social isolation.
Ms Leadbeater has “devoted much of her time to creating a positive legacy for her sister and has worked tirelessly to create as much positive energy and action from Jo's horrific murder,” her LinkedIn profile states.
In May her candidacy in the Batley and Spen by-election was confirmed.
In the lead-up to the 1 July vote, campaigning became increasingly hostile with Ms Leadbeater having been heckled and pursued on the campaign trail by a group claiming to represent Muslim parents, who voiced their opposition to Labour’s stance on LGBT+ rights.
“This is where I live, this is my community. Don’t come here and shout at me in the street. The Muslim community of Batley and Spen deserve better than this,” Ms Leadbeater told the main heckler in a video which was shared widely and came to define her campaign.
Speaking after her victory was confirmed on Friday morning, Ms Leadbeater said she hoped to do her sister proud as the new MP.
“It was a very big decision to put myself forward. It has been a very emotional campaign and today is very emotional for me for lots of reasons,” she told BBC Breakfast.
“But if I can be half the MP Jo was I know I will do her proud and I will do my family proud.”
Labour leader Sir Keir Starmer praised the new MP, saying she had “shown inspiring resilience in the face of hatred and intimidation”.
He added: “She was unafraid to call it out and ran a positive campaign of hope. Kim embodies everything I want the Labour Party to stand for: passionate about her local community and determined to bring people together.”
Brendan Cox, the widower of Ms Cox, said: ”She was incredibly brave to step forward into it, not just around the security side of things given what happened to Jo but also the context, it was a very bruising and pretty horrible campaign at times.“
Lord Mandelson said that Ms Leadbeater had ”embodied the politics of hope of reaching out beyond the sectarian division that it's communities against communities, just as her sister Jo Cox did”.
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