Brendan Cox later issued a statement on the beginning of a "more painful, less joyful, less full of love" new chapter for his family — but said his wife would have "no regrets" about her life.
"Jo believed in a better world and she fought for it every day of her life with an energy, and a zest for life that would exhaust most people," he said. "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."
Cox entered Parliament in 2015. She is a graduate of Cambridge University and worked for international campaign organizations, including Oxfam, prior to entering politics.
She drew on her experiences in war zones in a recent interview describing why she has continued to campaign over issues such as the conflict in Syria.
“I’ve been in some horrific situations," Cox told the Yorkshire Post. "That’s the thing that all of that experience gave me — if you ignore a problem it gets worse.”
Both sides of the debate suspended their campaigns after the attack to mourn Cox's loss.
News of the incident also sent shockwaves through the broader British political establishment, with lawmakers from all parties joining in to offer condolences and express their horror.
Jeremy Corbyn, head of the Labour Party, condemned the "horrific murder" and praised Cox's "lifelong record of public service" and "deep commitment to humanity."
"Jo Cox died doing her public duty at the heart of our democracy, listening to and representing the people she was elected to serve," Corbyn said in a statement. "We have lost a much loved colleague, a real talent and a dedicated campaigner for social justice and peace."
Cameron, the prime minister and the leader of the ruling Conservative Party, sent thoughts and prayers to Cox's family over the "tragic and dreadful news."
"We’ve lost a star," he said.
London Mayor Sadiq Khan said that in the year Cox was in Parliament "she made more impact than others make in a whole" career.
"She was the best of politics," he said in a statement. "I will miss her."
Presumptive Democratic nominee Hillary Clinton said in a statement that she was “horrified by the assassination” and that Cox was “a rising star.”
“It is cruel and terrible that her life was cut short by a violent act of political intolerance,” she said in the statement.
Oxfam, Cox's former employer, said she was “a passionate advocate for humanitarian issues including the conflicts in Darfur and the Democratic Republic of Congo.”
Cox worked for the organization between 2001 and 2009 and her husband while she worked there, according to a statement from the organization.
“She was an inspiring leader, really bringing the best out of all of us, always positive, always believing we could win, and always passionate for change,” Max Lawson, Cox’s former colleague, said in the statement.
Cassandra Vinograd is a Senior Writer and News Editor. Before joining NBC News, she worked as a London-based correspondent for The Associated Press and specialized in politics, foreign affairs and defense.
Vinograd previously worked as an editor for The Wall Street Journal in Brussels and London.
She has reported extensively from Afghanistan and on West Africa and the Middle East.
F. Brinley Bruton
F. Brinley Bruton is senior editor in charge of NBC News Digital’s London bureau.