Relatively young by political standards, Ms Cox is due to celebrate her 42nd birthday next Wednesday, and has been spoken of as a future Minister.
Ms Cox is a Remain supporter in the referendum and both official campaigns have suspended their operations as a mark of respect following the attack on her.
The MP for Batley and Spen, who is married with two children, graduated from Cambridge University in 1995 and went on to be head of policy for Oxfam, and work as an adviser for former Labour prime minister Gordon Brown’s wife, Sarah, and Baroness Kinnock.
Ms Cox has been a vocal advocate for the victims of the Syrian civil war and is chairwoman of the All Party Parliamentary Friends of Syria group.
The MP abstained in last autumn’s contentious vote on allowing British military action in Syria, insisting a more wide-ranging attempt at a solution to the conflict was needed.
Chair of the Labour Women’s Network, Ms Cox nominated Jeremy Corbyn for the Labour leadership contest last year, but voted for Blairite candidate Liz Kendall in the end.
Ms Cox later said she regretted helping Mr Corbyn get on the ballot paper, and pulled no punches after Labour’s poor performance in last month’s local and Scottish elections.
As the disappointing results rolled-in, Ms Cox told the BBC: “Jeremy needs to personally recognise that this isn’t good enough.
“He needs to take responsibility, he needs to set out a route map to power in 2020, and let’s rally first and foremost around the EU referendum.
“We need to look very hard at what’s gone wrong in the last eight months and put it right.”
Asked if she expected a leadership challenge, Ms Cox said: “Nobody is talking about that now and I don’t think it is the right course of action, but the clock is ticking.”
Ms Cox was also an advisor to the Bill and Melinda Gates Foundation, and to anti-slavery campaign group The Freedom Fund before entering parliament.
Despite growing up in the area, Tories attempted to paint Ms Cox as a candidate “parachuted” into Batley and Spen during the 2015 contest because she and her family’s London home was a converted barge moored near Tower Bridge.
But Labour insisted the Tories suffered from “candidate envy” as Ms Cox was registered to vote in the constituency and would divide her time between West Yorkshire and the capital if elected.
Ms Cox secured a majority of 6,057 in the general election, and fellow Labour MP John Mann remarked: “She is one of the stars of the new intake.”