The paper on the UK's role in the world was being compiled by the Labour politician in the weeks before she was killed in June.
Brendan Cox said his wife felt strongly the UK must "stand up" for civilians threatened by war and genocide.
The Cost of Doing Nothing has been published by think-tank Policy Exchange.
It warns the reaction to the Iraq war had prompted a rise in "knee-jerk isolationism, unthinking pacifism and anti-interventionism".
Withdrawing from the world stage posed "dangerous" implications for security and increased the risk of further global instability, it added.
Mr Cox said his wife had been passionately committed to the work, which was forged by her experiences of meeting survivors of genocide.
"Last week I was clearing some of Jo's things and found the first draft of the report that she had scribbled all over," he said.
"At the top she had written 'Britain must lead again'."
The report offers examples of successful interventions, such as the introduction of a no-fly zone in northern Iraq in 1991 to protect Kurds.
It also points to the consequences of doing nothing, such as the 1994 Rwandan genocide.
Mrs Cox had been working on a draft of the paper with Tom Tugendhat, the Conservative MP for Tonbridge and Malling.
He said: "To stand aside would not make us or the world safer, but leave us vulnerable to the whims of others rather than doing what we have always done - shape our own destiny and be a force for good."
The document was completed by Mrs Cox's friend Alison McGovern, the Labour MP for Wirral South.
She added: "Jo never believed that simply doing nothing in the face of atrocities was good enough, and neither should we."
Mrs Cox was shot and stabbed by Thomas Mair in Birstall in her West Yorkshire constituency. Her killer was jailed for life in November 2016.
Britain must not "shy away" from military action, according to a report worked on by murdered MP Jo Cox.