Naturally shy Jo stepped into the public arena as Jo Cox, MP for her home constituency of Batley and Spen, on a journey via Cambridge University and Oxfam, while her more outgoing sibling chose a smaller-scale, more private existence as a lecturer.
The events of June 16, 2016, when Jo was murdered outside her constituency officer in an attack that provoked global outrage and disgust, changed everything, not least the way the younger Leadbeater sister chose to make her mark in the world.
After the dust settled on the gruelling trial at the Old Bailey, which saw her sister’s killer handed a life sentence, the 40-year-old decided it was her moral duty to keep Jo’s memory and values alive.
While the MP’s widower Brendan honoured his wife’s memory at national level by promoting the Great Get Together community event, Kim decided to continue her work in the county where she grew up.
“We have had a horrific time, and it is one of the worst things that can happen to any family,” she told The Yorkshire Post.
“We have had to make some very difficult choices, but one of the choices we have made is to try and create something positive out of the horrendous thing that has happened.
“Part of that is to continue the work Jo was doing. I am not a political animal, I have no desire to get involved in party politics, and actually that was only a small piece of Jo and her life.
“Her life was very much about helping people, that is what she wanted to do, and she chose to go down the political avenue to do that. That is not something I have got any expertise or knowledge in.
“For me, it is about working with communities to try and improve community cohesion and promote positive relationships in our communities and help people who need help. Her background and her charity work in the voluntary sector is testament to that.
“What we are trying to do, Brendan is trying and I am trying with the support of my parents to create as much positivity out of what happened as possible.”
Speaking at her home in Gomersal this week, Kim is in the middle of organising one of the many events being held over the course of the year to promote her sister’s values of equality, tolerance and community cohesion.
A fundraising dinner in Cleckheaton, being held on Monday, has already brought in thousands for the More In Common campaign to raise money for causes close to Jo’s heart.
Later in the year there is a fun run on June 25, a bike ride from Spenborough to Parliament, and on June 29 an event at the stadium of Batley Bulldogs, who have donated the venue for the day to host workshops on music, arts and sport.
Perhaps most significantly, Kim hopes to work with schools in Batley and Spenborough, and ideally around Yorkshire, so that on June 16, the first anniversary of Jo’s death, the same assembly will be given on the positive lessons to be learned from the tragedy.
Kim and her parents are passionate about ensuring that her sister’s message, that what we have in common is stronger than what divides us, is promoted in Yorkshire.
“The kindness shown to us, since Jo was killed, the generosity of people, the kindness of spirit, that is what we should be talking about, because that is what Yorkshire is about”, she said..
“Yorkshire is not about the odd, isolated, horrendous incident, it is about wonderful kind, generous people, and if I can do anything to promote that then I am doing something good.”
This generosity of spirit in Yorkshire, especially her local area, was clear to see in the days after Jo was killed.
“People round here have been so kind and supportive, whether it is people who have stopped me in the supermarket, while going for a walk, people will stop you and be so lovely to you. All anyone wants to do is to try and help.
“Nobody can change what happened, and everyone knows that, and has that sense of helplessness in that respect, but what everyone wants to do is try and create something positive. When Jo was killed, stuff just kept arriving at the house.
“There would be flowers, presents for the children, there would be cards, books of condolence. I had to get the loft boarded out to store it all. My mum’s house, on the boat, there were flowers everywhere.
“People have knitted things up in Scotland, someone from Australia sent something, literally from across the world, that is what humanity is about. That kept us going. Someone named a star after Jo.
“There were random acts of total kindness because no-one knew what to do and could see how horrendous it was.
“The stuff people did was unbelievable. The awards and things like that people have done since, the primary schools in the area, the Jo Cox kindness award.
“The variety business awards did an award in Jo’s name, all over we have been asked to do so many things because people want to honour what Jo did. The reality is, doing what Jo did, she would have worked for the next 40 years, and made a difference to a lot of people’s lives.
“This is where I feel I have a moral obligation to do the sort of work she would have done, because she can’t do it herself any more.”
The days and weeks after Jo’s death saw her family struggle to make sense of what happened, and Kim herself presented with a surprising opportunity.
“What was hard for me was that I had people, eminent politicians, saying it would be great if I wanted to be the next MP and it was something I should consider,” she said.
“It wasn’t my world, it was Jo’s world, I am not a political animal, I supported Jo because she was my sister and I think people locally found this quite hard to understand.
“But you do doubt yourself and think ‘maybe I should be the next MP, maybe that is the answer’. Thank God you don’t make decisions when you are so emotionally vulnerable and raw. Because I could have agreed to do anything.”
And while the first anniversary of her sister’s death will see community activities taking place around the country, Kim is unsure how the enormity of the day will affect her personally.
She said: “It’s hard to say because you don’t know how you are going to feel. It’s wonderful we are being so positive, but the reality is that on the day it’s hard.
“What I have got to be careful about is not over-committing, because you don’t know how you are going to feel on that day. I am not sure what we will do on that day.
“What I would encourage as many people as possible to do over that period, June 16,17 and 18, is, Jo loved a party, go and have a good time. Jo loved a party, get together with your friends and family and appreciate each other try and be really positive, because, and this is what motivates me with pretty much everything, that is what Jo would want me to do.
“She would also totally understand the days when I need to cry and look after myself in a very private manner, but ultimately, she would say if you feel you have the strength to do it, go and do something positive.
“Brendan and I know that is what Jo would be saying. She would be devastated if she knew this had broken me and had created any more devastation than it has to. She would be saying, Kim, you have to try and turn it around.”