Brendan Cox will pay tribute to his wife and touch on the “awful year for our family” in the Channel 4 broadcast on December 25.
But he will also tell viewers that now is the “moment to reach out to somebody that might disagree with us”.
Mrs Cox was shot and stabbed to death by neo-Nazi Thomas Mair in her Batley and Spen constituency days before June’s EU referendum.
The 41-year-old, the mother of two young children, was an outspoken critic of strategic policy in Syria and a humanitarian who campaigned for women’s rights around the world.
Her husband of seven years recorded the tribute on the converted Dutch barge which the family called home.
In the message, which is traditionally billed as an alternative to the Queen’s annual Christmas Day address, Mr Cox will say: “Jo loved Christmas, the games, the traditions, the coming together of friends and family and above all the excitement of our kids.
“This year we’ll try to remember how lucky we were to have Jo in our lives for so long - and not how unlucky we were to have her taken from us.
“2016 has been an awful year for our family, and it’s been a divisive one for the wider world.”
He will say that “fascism, xenophobia, extremism and terrorism” had made the world “divided” and feel “threatened” and that “these trends could threaten the fundamental freedoms, and democracy that our grandparents fought for”.
But he will add: “That isn’t how it has to be.
“Just as it has become apparent that tolerance and tolerant societies are only as strong as their defenders - there is nothing inevitable about the rise of hatred.
“Instead of being a turning point for the worse, 2016 could be a wake-up call that brings us back together.”
Mr Cox will say that his wife quoted the philosopher Edmund Burke, who said that all that is necessary for evil to triumph is for good men and women “to do nothing”, just a few weeks before she died.
Her widower will say “that has never been more true”.
The need to defend tolerance and fair play “isn’t someone else’s problem,” he will add.
Channel 4 has broadcast a Christmas Day message since 1993.
In previous years it has been delivered by whistle-blower Edward Snowden, the parents of murdered London teenager Stephen Lawrence, campaigner Katie Piper and reality star Sharon Osbourne.
Making the announcement yesterday, Channel 4’s deputy head of news and current affairs Daniel Pear said: “2016 has been one of the most momentous years in recent history - punctuated by political turmoil, conflict and a stream of dramatic events.
“Brendan’s message references this wider turbulence but is also a very personal reflection at Christmas, a time for family and looking back over the past year, from a man who has suffered the tragic loss of his wife and mother of his children as a result of extremism.”
Earlier this week, Mr Cox hit out at Nigel Farage on Twitter over the former Ukip leader’s response to the suspected terrorist attack in Berlin.
Brendan Cox warned Mr Farage was heading for a “slippery slope” after the right-wing politician linked the carnage in the German capital with Chancellor Angela Merkel’s policies.
But Mr Farage doubled down when he appeared on radio on Tuesday morning, saying Mr Cox “would know more about extremists than me”. The comment prompted hundreds of retweets and replies.