Jo Cox, 41, was elected to the House of Commons last year and represented a constituency in Yorkshire, northern England, for the main opposition Labour Party.
She was previously an adviser to Sarah Brown and Glennys Kinnock, the wives of two former Labour Party leaders. She also worked with several charities, including Oxfam, Save the Children, the Bill and Melinda Gates Foundation, and anti-slavery group The Freedom Fund.
Cox, who chaired the Labour Women's Network, had made finding a solution to the Syrian civil war a top priority. She was critical of Britain's reluctance to deepen its military involvement against Islamic State extremists, but abstained in a vote on air strikes because she said the plan didn't devote enough attention to stopping the "brutality" of President Bashar Assad.
In recent weeks she had been campaigning for Britain to remain in the European Union ahead of the country's June 23 referendum.
She initially backed Jeremy Corbyn for the Labour leadership, but later said she regretted that decision and instead voted for one of his opponents, Liz Kendall.
Cox graduated from Cambridge University in 1995. The first in her family to graduate from a university, she described her years at Cambridge as difficult, telling the Yorkshire Post that is where she realized that "where you were born matters."
Married and with two children, she divided her time between a houseboat on the River Thames in London and a home in her constituency, Batley and Spen. Her personal webpage says she enjoyed running, cycling and mountaineering.