Ms Leadbeater, sister of the murdered MP Jo Cox, retained the seat for Labour narrowly defeating Conservative candidate Ryan Stephenson by a slim margin of just 323 votes.
Halifax MP Holly Lynch, who herself has had strong connections with Batley and Spen over the past few years and helped to run Labour's campaign in last week's by-election, said she is looking forward to working with Ms Leadbeater in Parliament.
Ms Lynch said: “I became the supervising MP for Batley and Spen following Jo‘s tragic murder in 2016.
“Since then I’ve had the chance to get to know Batley and Spen as a neighbouring MP, as well as working with Kim at The Jo Cox Foundation.
“It has been a pleasure to work with her once again and I’m delighted that the people of Batley and Spen have a representative who understands the area, cares about it deeply, and will work with everyone to fight for its future.
“As a fellow West Yorkshire MP, I’m really looking forward to working with her to make sure our part of the world gets the resources, the funding and the recognition it deserves from Government.”
Ms Lynch has been praised within the party for leading Ms Leadbeater’s campaign and helping to secure a much-needed victory for Labour after disappointing recent results in other parts of the country.
West Yorkshire Metro Mayor Tracy Brabin, who stepped down as Batley and Spen MP in early May, said Ms Lynch “fought like a tiger”.
Barry Sheerman, Huddersfield MP, tweeted: “Very proud of the seriously outstanding work of my friend and colleague Holly Lynch MP in this tough by-election battle.”