
Cox, who was the MP for Batley and Spen, died after being shot and stabbed following a local surgery with constituents in Birstall, West Yorkshire.
Before being elected to parliament at the May 2015 general election, Cox held a number of roles in the voluntary sector, including a couple of spells with major children's charities.
In 2012, she worked as a strategy consultant on campaigns at both Save the Children and the NSPCC.
Save the Children interim chief executive Tanya Steele, said: "Our heartfelt thoughts are with the family of Jo Cox.
"She has been a great friend and supporter of Save the Children, fighting for the rights of children here in the UK and around the world.
"As a Member of Parliament, she was an outspoken advocate for the children of Syria. At this terrible time, our sincere condolences go to Jo's husband Brendan, who was Save the Children's director of policy and advocacy until last year."
Peter Wanless, chief executive of the NSPCC, said: "Jo was passionate about helping children and families who face adversity. She had a great understanding of the problems young people face and was totally committed to changing things to improve their lives.
"Jo impressed everyone with her ceaseless drive, determination and, above all, compassion during her time working at the NSPCC as a strategy consultant.
"Our thoughts are with her family and friends who must be absolutely devastated by her tragic death."
From 2009 to 2011, Cox was director of a global campaign to prevent women and babies dying in pregnancy and childbirth, on which she worked alongside Sarah Brown, wife of the former Prime Minister.
Prior to this, she spent seven years at Oxfam, where she held several positions including head of policy and advocacy, and head of humanitarian campaigning.
Martin Houghton-Brown, chief executive of youth homelessness charity Depaul UK, said: "Jo Cox was a tireless campaigner who was committed to the fight against homelessness and was recently elected as vice-chair of the newly formed All Party Parliamentary Group on Ending Homelessness, to which Depaul contributes.
"The tragic loss of someone who believed in making a better world and who deeply cared and battled for the least fortunate in society including the homeless has deeply affected us all."
David Mackintosh MP, Chair of the All Party Parliamentary Group on Ending Homelessness, said: "Jo was instrumental in the setting up of the APPG on Ending Homelessness. She was an incredibly intelligent and spirited MP.
"It is with deepest sympathy that we must come to terms with her horrendous and senseless murder. We will carry on the great work that Jo started to make her goal of ending homelessness a reality."
Police have arrested a 52-year-old-man over the incident in Birstall.
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