In the weeks before she was shot and stabbed by a neo-Nazi, the Labour backbencher had started to write a joint paper with Conservative Tom Tugendhat about the UK’s role in the world.
Widower Brendan Cox said his wife wrote “Britain must lead again” on a draft of the report.
The backlash over the Iraq war had led to a rise in “knee-jerk isolationism, unthinking pacifism and anti-interventionism”, according to The Cost of Doing Nothing paper. But it wants that retreating from the global stage has “dangerous” implications for national and international security and heightens the risk of further global instability.
Mr Cox said: “Jo was passionate about this piece of work. She felt deeply that the UK had a duty to stand up for civilians threatened by war and genocide.
“Her commitment wasn’t theoretical, it was forged by her experience of meeting survivors of genocide in Kosovo, Bosnia, Rwanda and Sudan.
“Last week I was clearing some of Jo’s things and found the first draft of the report that she had scribbled all over. At the top she had written ‘Britain must lead again’. Although she isn’t here to advance that argument, she’d be delighted that her colleagues and friends are able to do so in her stead.”
The report, completed by friend Alison McGovern MP and published by Policy Exchange, highlights examples of successful intervention such as Nato’s action in 1990 to shield civilians in Kosovo from ethnic cleansing.
It also sets out the “devastating consequences” of failing to take action, including the 1994 Rwandan genocide and Syrian civil war.
Co-author Mr Tugendhat said: “Britain has never been isolationist. It is in our national interest to be engaged with the world we helped shape.
“That means taking responsibility, and influencing events and intervening when necessary. To stand aside would not make us or the world safer, but leave us vulnerable to the whims of others.”
Ms McGovern, MP for Wirral South, said: “We cannot simply look the other way in cases of war crimes, crimes against humanity or genocide. Jo never believed that simply doing nothing in the face of atrocities was good enough, and neither should we.”
Mrs Cox, 41, had worked as head of policy and advocacy at Oxfam and became MP for Batley and MP in May 2015.
The mother-of-two was killed in June while she was on the way to one of her regular constituency surgeries in Birstall Library.
Former Prime Minister Gordon Brown, who will launch the report, said: “In her last speech in the House of Commons, Jo Cox said that ‘sometimes all it takes for evil to triumph is for good men to do nothing’.
“Nothing is more important than the responsibility of each state to protect their populations from genocide, war crimes, crimes against humanity and ethnic cleansing, and the responsibility of the international community to act if a state is unwilling or unable to do so.”
It was revealed this week that a fund established in Mrs Cox’s memory has raised almost £2m.
The first £1.5m will be shared by three charities close to her heart, with the rest funding a foundation to advance the values and causes for which she fought.