Here, we reproduce some of the tributes, just a small sampling of an overwhelming outpouring of grief at the loss of a politician destined for greatness, and the deeply personal mourning of a mother of two young children.
Brendan Cox, Jo’s husband
“Today is the beginning of a new chapter in our lives. More difficult, more painful, less joyful, less full of love.
“I and Jo’s friends and family are going to work every moment of our lives to love and nurture our kids and to fight against the hate that killed Jo.
“Jo believed in a better world and she fought for it everyday of her life with an energy and a zest for life that would exhaust most people.
“She would have wanted two things above all else to happen now, one that our precious children are bathed in love and two, that we all unite to fight against the hatred that killed her.
“Hate doesn’t have a creed, race or religion, it is poisonous.
“Jo would have no regrets about her life, she lived every day of it to the full.”
Prime Minister David Cameron
“This is absolutely tragic and dreadful news and my thoughts are with Jo’s husband Brendan, their two children and wider family. We’ve lost a great star. She had a big heart and people are going to be very, very sad at what has happened.
“She was a very strong campaigning MP. She had a great track record of caring about refugees and had taken a big interest in how we can look after Syrian refugees and do the right thing in our world. She was a star for her constituents, a star in Parliament and a star right across the House.
“It’s right that we are suspending campaigning activity in this referendum and everyone’s thoughts will be with Jo’s family and her constituents at this terrible time.”
Labour leader Jeremy Corbyn
“The whole of the Labour party and Labour family - and indeed the whole country - will be in shock at the horrific murder of Jo Cox today.
“Jo had a lifelong record of public service and a deep commitment to humanity. She worked both for Oxfam and the anti-slavery charity, the Freedom Fund, before she was elected last year as MP for Batley and Spen – where she was born and grew up.
“Jo was dedicated to getting us to live up to our promises to support the developing world and strengthen human rights – and she brought those values and principles with her when she became an MP.
“Jo died doing her public duty at the heart of our democracy, listening to and representing the people she was elected to serve. It is a profoundly important cause for us all.”
Will Straw, Executive Director of Britain Stronger In Europe, the main Remain campaign group
“Jo Cox was a good friend and my thoughts are with her husband, Brendan, and her two small children, Cuillen and Lejla. She was a wonderful woman, dedicated campaigner and a hard-working MP. Inside and outside Parliament, Jo had fought for a more peaceful and just world. It is senseless that her life should be cut short in such a brutal manner.
“This tragedy has shocked everyone in the campaign and especially those in Yorkshire who had been working with her. In light of this awful news, we have suspended our campaign for today and tomorrow.”
Labour deputy leader Tom Watson
“The whole of the Labour movement is devastated at Jo’s death. We have lost a colleague so young who had much more to contribute to public life. She was our future.
“It is hard to comprehend how a compassionate, principled and beautiful person can be taken away from us so cruelly. It’s even more devastating because she was doing what she did best - serving her constituents.
“We grieve her loss. Our love and prayers are with Brendan and Jo’s family.”
Leeds City Council leader Judith Blake
“Our thoughts and deepest sympathies are with Jo’s family and friends at this truly awful time. This is an absolutely shocking incident that has robbed a family of a loving mother and wife who was simply doing her job, representing the people of Batley and Spen.
“This is a tragedy which cannot be allowed to undermine our democratic processes, processes that Jo was so proud to represent. Leeds as a neighbour stands united with Kirklees and our thoughts remain with Jo’s family as they try to come to terms with their dreadful loss.”
The next door neighbours of murdered MP Jo Cox spoke of a ‘down to earth girl next door’ and paid tribute to her as an MP.
Helen Skelly, who lives in Heckmondwike, lived next to the Cox family for several years and described them as “a lovely family.”
The retired nurse said: “They moved in when the kids were teenagers. Jo’s parents, Jean and Gordon were easy to get along with and would always say hello. The girls, Jo and Kim [her younger sister] both went to Heckmondwike Grammar School. I didn’t see them a lot but they always had a smile and a pleasant word to say, they would always ask about your family and how you were.
“Jo was really down to earth but outgoing. She knew what she wanted from the word go. I just cannot believe this has happened and my heart goes out to her parents and sister and the rest of her family, who must be going through absolute hell. She was the girl next door.”
She added: “What has happened is ridiculous, it’s just a mile away from where we live.”
Kirklees Council Chief Executive Adrian Lythgo
“We always knew that so many people had great respect for Jo, and how influential she was in conversations and in debate. But that has only been reinforced by the reaction to her tragic death.
“Party colleagues and opposition members have all been united in their shock and sadness at what would have been a stellar career cut short in the worst way.”
Nick Clegg, Sheffield Hallam MP and former Deputy Prime Minister
“Jo Cox was unusually free of the tribal pettiness of politics - always friendly, cheerful and kind to friend and foe alike.
“My heart goes out to her family. A lovely person’s life has been snuffed out by hate.”
London Mayor Sadiq Khan
“Everyone who met Jo knew she was special. I knew her from her time as a fearless campaigner working on behalf of some of the world’s poorest and most marginalised people and helped her, a little, in her campaign to become the Labour candidate and MP for Batley and Spen. I knew that she would bring all her passion for social justice and equality to Parliament and fight just as hard for her own community in Westminster as she has for so many others around the world.
“In the year she was an MP she made more impact than others make in a whole parliamentary career. Jo loved being the Member of Parliament for Batley and Spen. She was the most powerful advocate for the people of Syria, ensuring their plight stayed on the political agenda as well as reminding us all of our country’s proud record of humanitarianism and brought her expertise to bear on some of the most pressing global challenges of our time. But she was also an extremely hard-working local MP for her home constituency and so proud of her roots there.
“Jo was one of the smartest and most independently minded MPs, respected by people from all parties. She was also warm and funny – I remember her telling me recently that she was going to get permission from the House of Commons to park her little boat at Parliament so she could drive it to work.
“It is typical of Jo that she was serving her community today, doing what she loved, when this horrific attack happened. She was the best of politics, the best of Labour and I will miss her. All my thoughts and prayers are with her husband Brendan, her two little children, and her whole family.”
Labour frontbencher Harriet Harman
“Jo’s death is an absolute tragedy. She was dynamic and fearless. Elected only a year ago she was a beacon among the new generation of young Labour women MPs. So full of promise for the future, so committed to progressive politics. Jo’s politics were always about bringing people together and never about creating divisions.
“She put into practice her belief that politicians must be amongst the people they represent and she was, in every town, village and community in her constituency.
“We were immensely proud of her and are devastated by her loss.”
She added: “Her children will now have to grow up without their mother but we will make sure that they know what an amazing, progressive and principled politician their mother was and how much we admired her.
“My deepest sympathy goes to Brendan and to Jo’s family.”
Labour MP for Barnsley Central, Dan Jarvis
“Devastated at the loss of brilliant, funny & determined friend Jo Cox, who dedicated her life to helping others. Love to her family.”
Former Labour leader Ed Miliband tweeted: “My heart breaks for the loss of Jo Cox and for Brendan and their kids. She was so full of life and joy. Words feel hopeless right now.”
Kevin Barron, Labour MP for Rother Valley
“Thoughts & prayers with Jo’s husband Brendan, two young children, family & friends.”
Yvette Cooper, Labour MP for Pontefract and Castleford
“One of liveliest, bravest & most passionate MPs. Thoughtful, creative, determined. Cannot believe we have lost you.”