On 16 June 2016, Jo Cox, a British Labour Party politician and Member of Parliament (MP) for Batley and Spen, died after being shot and stabbed multiple times in Birstall, West Yorkshire.

[6] On 16 June 2016, Cox was on her way to meet constituents at a routine surgery in Birstall, West Yorkshire, when Thomas Mair shot her twice in the head and once in the chest with a modified .22 hunting rifle then stabbed her fifteen times outside a library on Market Street.

[18] Mair was arrested about a mile from the murder scene unarmed[19] by police constables Craig Nicholls and Jonathan Wright, who were later awarded the Queen's Gallantry Medal.

[24][27] He had searched the internet for information about the British National Party, South African apartheid, the Ku Klux Klan, prominent Jewish people, matricide,[22][30] white supremacy/nationalism, Nazism/Nazi Party, SS/Waffen SS, Israel, mass shootings, serial killers, Frazier Glenn Miller Jr., William Hague, Ian Gow (another assassinated MP),[24] and Norwegian far-right terrorist Anders Behring Breivik (about whose case he collected newspaper clippings).

[24] The evening before killing Cox, Mair visited a treatment centre in Birstall seeking help for depression; he was told to return the next day for an appointment.

[24] In October 2020, a press report stated that West Yorkshire Police's Homicide and Major Enquiries Team continued to investigate how he acquired the weapon used, which remains a mystery.

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

"[56] Rosena Allin-Khan, who won the Tooting by-election for Labour, used her victory speech to pay tribute to Cox, saying, "Jo's death reminds us that our democracy is precious but fragile.

"[53] One day after the attack, Corbyn and Prime Minister David Cameron visited Birstall, where they joined locals to lay floral tributes to Cox.

[58]Veteran Labour politician Neil Kinnock, whose wife Glenys had supported Cox's candidacy and whose son Stephen shared an office with her, described the family's grief in a BBC television interview.

[59] Writing for the Financial Times, Sarah Brown, who worked with Cox on a campaign to reduce the number of deaths in pregnancy and childbirth, said, "Jo's life testified to her view that tolerance is not enough.

[65] Friends organised "More in Common – Celebrating the life of Jo Cox", a public event in her remembrance held in Trafalgar Square, London, on 22 June – the date of her 42nd birthday.

[69][70] Musicians and festivalgoers at Glastonbury, held later that week, also paid tribute to Cox; at one concert Billy Bragg led the audience in a rendition of "We Shall Overcome" and was joined on stage by women wearing suffragette ribbons.

[91] The Great Get Together was also supported by former British Prime Ministers John Major, Tony Blair, Gordon Brown, and David Cameron, all of whom who recorded a joint video paying tribute to Cox and urging people to celebrate her life.

[92] On 24 June 2017, a coat of arms designed by Cox's children was unveiled by them at the House of Commons, where MPs killed in office are remembered by heraldic shields.

[93] Rock group U2 paid tribute to Cox during the UK leg of their 2017 Joshua Tree Tour; lead vocalist Bono, who had worked with her on the Make Poverty History campaign, dedicated the song "Ultraviolet (Light My Way)" to her memory.

United States President Barack Obama telephoned Cox's husband to offer condolences on behalf of the American people,[95] and invited the family to meet him at the White House.

"[97][98] Several European leaders expressed their shock at the news, among them German Chancellor Angela Merkel, who described the attack as "terrible" and called for a moderation of language to counter radicalisation and to foster respect.

[101] Numerous other tributes were paid to Cox, including those by public figures in Australia,[102] Canada,[101][103] Czech Republic,[104] Finland,[105] France,[55] Greece,[106] Ireland,[106][107] Italy,[99] Netherlands,[108] New Zealand,[100][109][110] the PLO,[111] Spain,[56] Sweden[112] and the United States.

Earlier that year, Cox had written to the Committee praising the work of the civilian voluntary emergency rescue organisation known as the White Helmets, and nominating them for the prize.

The nomination gained the support of twenty of her fellow MPs and about twelve high-profile personalities including George Clooney, Daniel Craig, Chris Martin and Michael Palin.

[121] Only two British newspapers did not feature a picture of Cox on their front pages as her murderer was arrested: the Financial Times, which focused on the first autumn statement from the Chancellor of the Exchequer, Philip Hammond; and the Daily Mail.

By describing the murder in the context of Nazism, the judge separated the sentiments from modern political discourse , giving a "free pass" to contemporary extremist groups, public figures and press whose rhetoric were likely to have influenced Mair.

[133] In July 2016, Kevin McKeever, a Labour politician and partner in Portland Communications – a public relations firm accused of playing an instrumental role in an attempt to force the resignation of Jeremy Corbyn – received an alleged death threat telling him he should "prepare to be coxed".

[136] Cox's murder was also explicitly referenced in the social media posts of a man who was jailed for four months in April 2017 for making death threats towards the then-MP for Eastbourne Caroline Ansell of the Conservative party.

"[138] At the time of Cox's death, MPs wishing to make additional security arrangements were required to apply to the Independent Parliamentary Standards Authority (IPSA), the watchdog overseeing their expenses.

[154] In the days after Cox's death, Arron Banks, founder of the Leave.EU campaign for Britain's withdrawal from the European Union, conducted private polling to determine whether the incident would affect the referendum's outcome.

"[155] Likewise, Gary Jones of the Mirror pressurised political editor Nigel Nelson to write a front-page Mirror story on "the Jo effect", saying her death had swung support to Remain in a new opinion poll under the headline: "Tragic Jo's Death Sparks Poll Surge" despite only 192 of the 2,046 answers ComRes received being after the murder and that ComRes stating, "the figures should be treated with a degree of caution given the sample size".

[156] At a speech to the London School of Economics in September 2016, Martin Schulz, the President of the European Parliament, said the "nasty" referendum debate was a contributing factor in Cox's death.

The comments were swiftly criticised by some of Cox's colleagues, including leading Eurosceptic Conservative politician Jacob Rees-Mogg, who described them as "trivialising" her death.