"In the Dark Streets Shineth: A 1941 Christmas Eve Story" is on sale now.
It tells the story of how the two world leaders met during one of the bleakest holidays in modern history, its publishers noted.
"Just days after the Japanese attack on Pearl Harbor, Churchill and Roosevelt met privately," Shadow Mountain Publishing said in a news release. "Later that evening, from the balcony of the White House at the lighting of the national Christmas tree, the two leaders delivered a powerful message to an anxious crowd -- a message that uplifted an entire nation during a time of great uncertainty."
"This is a strange Christmas Eve," Churchill told the crowd of 20,000. "Almost the whole world is locked in deadly struggle. ... Let the children have their night of fun and laughter. Let the gifts of Father Christmas delight their play. Let us grown-ups share to the full in their unstinted pleasures before we turn again to the stern task and the formidable years that lie before us."
McCullough is best known for his biographies of U.S. Presidents Harry Truman and John Adams.