[3] Cox became a campaigner on issues relating to the Syrian civil war, and founded and chaired the all-party parliamentary group Friends of Syria.

On 16 June 2016, Cox died after being shot and stabbed multiple times in the street in the village of Birstall, where she had been due to hold a constituency surgery.

[15] While there, she helped to publish For a Safer Tomorrow, a book authored by Ed Cairns which examines the changing nature of the world's humanitarian policies.

[22] Cox was nominated by the Labour Party to contest the Batley and Spen seat being vacated by Mike Wood at the 2015 general election.

[29] In October 2015, she co-authored an article in The Observer with Conservative MP Andrew Mitchell, arguing that British military forces could help achieve an ethical solution to the conflict, including the creation of civilian safe havens in Syria.

[31][32] In the Commons vote in December to approve UK military intervention against ISIL in Syria, Cox abstained because she believed in a more comprehensive strategy that would also include combatting President Bashar al-Assad and his "indiscriminate barrel bombs".

"[33] Andrew Grice of The Independent felt that she "argued forcefully that the UK Government should be doing more both to help the victims and use its influence abroad to bring an end to the Syrian conflict.

"[34] In February 2016, Cox wrote to the Nobel Committee praising the work of the Syrian Civil Defense, a civilian voluntary emergency rescue organisation known as the White Helmets, and nominating them for the Nobel Peace Prize, stating: "In the most dangerous place on earth these unarmed volunteers risk their lives to help anyone in need regardless of religion or politics."

The nomination was accepted by the committee, and garnered the support of twenty of her fellow MPs and several celebrities, including George Clooney, Daniel Craig, Chris Martin and Michael Palin.

[35][36] Cox, a supporter of the Labour Friends of Palestine and the Middle East,[37] called for the lifting of the blockade of the Gaza Strip.

[38] She opposed efforts by the government to curtail the Boycott, Divestment and Sanctions movement, and said: "I believe that this is a gross attack on democratic freedoms.

Following her death, Tugendhat wrote in The Times: "Our starting point was that while Britain must learn the painful lessons of Iraq, we must not let the pendulum swing towards knee-jerk isolationism, ideological pacifism and doctrinal anti-interventionism.

"[40] With the charity Tell MAMA she worked on The Geography of Anti-Muslim Hatred, investigating cases of Islamophobia; the report was dedicated to her at its launch on 29 June 2016.

[15] The BBC cancelled editions of Question Time and This Week, two political discussion programmes scheduled to air that evening focusing on issues relating to the referendum.

[48] The Cox family divided their time between their constituency home and a houseboat, a converted Dutch barge, on the Thames, moored near Tower Bridge in London.

"[56] Four hours after the incident, West Yorkshire Police announced that Cox had died of her injuries shortly after being admitted to Leeds General Infirmary.

[68] As confirmed by the Crown Prosecution Service, Mair's conviction for a crime amounting to a terrorism offence also means he is officially considered a terrorist by the United Kingdom.

"[74] US President Barack Obama telephoned Cox's husband to offer his condolences, noting that "the world is a better place because of her selfless service to others.

[82] On the evening of 23 June, while ballots were being counted in the EU membership referendum, polling officials in the Yorkshire and Humber region observed a minute's silence.

[85] The funeral, "a very small and private family affair",[86] was held in her constituency on 15 July, with many thousands of people paying their respects as the cortege passed.

Labour candidate Tracy Brabin, an actress whose credits include a role in Coronation Street in the mid-1990s, won the by-election with 86 per cent of the vote.

Bernard Kenny, a passerby who tried to stop Mair during the attack and was himself stabbed in the stomach, was awarded the George Medal, which is given to civilians who exhibit great bravery.

[106] Out of respect for Cox, at the 2016 Batley and Spen by-election parties with parliamentary representation did not stand against Labour candidate Tracy Brabin who was elected with an 85.8% majority.

On 2 July 2021, Jo Cox's sister Kim Leadbeater, who declared that she had not previously been a political person but 'cared deeply' about where she had been born and grew up, was elected in the 2021 Batley and Spen by-election.

On 24 June 2017, a coat of arms, designed with the input of Cox's children, was unveiled by her family at the House of Commons, where MPs killed in office are honoured with heraldic shields.