His mother, Effie (McKinlay) Kantor, worked as the editor of the Webster City Daily News during part of his childhood.

His father, John Martin Kantor, was a native-born Swedish Jew descended from "a long line of rabbis, who posed as a Protestant clergyman".

[6] His grandson, Tom Shroder wrote a biography of his grandfather titled, The Most Famous Writer Who Ever Lived: A True Story of My Family.

[4] He was an early resident of Free Acres, a social experimental community developed by activist Bolton Hall in Berkeley Heights, New Jersey.

[7] In two years, he sold 16 short stories and a serialized novel to Howard Bloomfield, editor of Detective Fiction Weekly.

[citation needed] It was during this decade that Kantor first wrote about the American Civil War, beginning with his novel Long Remember (1934), set at the Battle of Gettysburg.

As a boy and teenager in Iowa, Kantor had spent hours listening to the stories of Civil War veterans, and he was an avid collector of first-hand narratives.

After flying with some bombing missions, he asked for and received training to operate the bomber's turret machine guns, although he was not in service and this violated regulations.

[10][11] After selling the movie rights to his novel, Kantor was disappointed that the film was released under the title The Best Years of Our Lives (1946), and that details of the story had been changed by the screenwriter Robert Sherwood.

Beginning in 1948, Kantor arranged an intensive period of research with the New York City Police Department (NYCPD).

These experiences informed most of his short crime novels, as well as his major work Signal Thirty-Two, published in 1950 with jacket art by his wife Irene Layne Kantor.

[13] During his assignment with the U.S. troops in World War II, Kantor entered the Buchenwald concentration camp as they liberated it on April 14, 1945.

As he struggled to understand, he developed ideas which he expressed in his novel, where he portrayed some civilian Southerners sympathetically, in contrast to officers at the camp.

He wrote two works for young readers set in the Civil War years: Lee and Grant at Appomattox (1950) and Gettysburg (1952).

In the November 22, 1960, issue of Look magazine, Kantor published a fictional account set as a history text, titled If the South Had Won the Civil War.