The pledge was signed outside Jo Cox House in Batley, close to where the former MP was murdered during the 2016 EU referendum campaign.
It commits the candidates to:
- Take responsibility for setting an appropriate tone when campaigning;
- Lead by example to encourage and foster constructive democratic debate and tolerance of other points of view;
- Promote and defend the dignity of others, including political opponents, treating all with courtesy and respect.
They were joined by Kim Leadbeater, Mrs Cox's sister, as they signed.
Ms Leadbeater said: “My sister believed in robust political debate, but she also believed that we can debate our differences without abuse or personal attacks. It means a great deal to my parents and me that the candidates here in the constituency that Jo loved so much have signed up to the kind of politics she represented.
“Here in Batley and Spen we know the price of hatred and political violence, but this is a call that I believe should be taken up by candidates all across the country. I hope desperately that in a few weeks time we will be able to look back on an election that upheld the standards of decency and respect that our democracy was once famous for and can be again.”
Ms Leadbeater, said she hoped candidates across the country would now follow their lead.
She said: “I had hoped that the murder of my sister Jo would lead to a better way of doing politics, but sadly that hasn’t always been the case. So this is the opportunity for us here in Batley and Spen to send a clear message to the country about the kind of democracy we all want."
"As a community, we know the cost of political violence and it's very important that we ensure that no family has to go through what we've been through ever again," she added.
"I think the starting point for that is leadership, and the people standing for public office showing a sense of responsibility.
"I think what has happened unfortunately in the last few years is that we've lost our way a little bit in terms of having robust, passionate and civilised debate.
"Some of the discussions have transcended into insults, personal attacks and, on some occasions, violence.
"I think we need to pull back from that, so what we're asking people to do, across the political spectrum, is sign up to a pledge saying they will conduct themselves in this General Election campaign in a respectful and civilised manner."
Mrs Cox, a mother-of-two, was elected as Batley and Spen MP in 2015, holding the seat until her murder by Thomas Mair on June 16 2016.
The Jo Cox Foundation is working with the Committee on Standards in Public Life to agree a Joint Standard of Conduct with all political parties that would apply not only during election campaigns but at all times.
Catherine Anderson, Chief Executive of the Foundation, said: "This pledge signed in Batley is a great first step.
"We all value vigorous political debate and freedom of speech but that should not extend to abusive behaviour designed to intimidate and silence people.
"It threatens our democracy itself. From our discussions with all the parties we know that they recognise the importance of restoring civility and respect to our public discourse and we look forward to working with them and with the committee to agree a long-term standard of behaviour.”