Benjamin McKinlay Kantor was born and grew up in Webster City, Iowa, the second child and only son. He had a sister Virginia. His mother was Effie McKinlay Kantor, who was the editor of the Webster City Daily News during part of his childhood. His father, John Kantor, abandoned the family before Benjamin was born. Afterward his mother moved with her children to the home of her parents, Mr. and Mrs. Adam McKinlay, in the same city.

As a child, McKinlay started using his middle name as his given name. He changed its spelling, adding an "a" because he thought it sounded more Scottish as MacKinlay, and chose to be called "Mack" or MacKinlay. He attended the local schools and made full use of the Kendall Young Library, which he described as his "university". Mack Kantor won a writing contest with his first story "Purple".

In 1928, Kantor published his first novel, Diversey, set in Chicago about its gangsters.

In the 1930s, Kantor first wrote about the American Civil War in his novel Long Remember (1934). Kantor had spent hours listening to the stories of Civil War veterans when he was young, and he was an avid collector of first-hand narratives. Long Remember is one of the first realistic novels published about the Civil War. In writing more than 30 novels, Kantor often returned to the theme of the American Civil War. He won the Pulitzer Prize for his novel Andersonville (1955), about the Confederate prison camp. Additional works set in the war years included Lee and Grant at Appomattox (1950) and Gettysburg (1952), both for young readers.

During World War Two, Kantor reported from London as a war correspondent for a Los Angeles newspaper. After flying with some bombing missions, he asked for and received training to operate the bomber's turret machine guns (this was illegal, as he was not in service). Kantor interviewed numerous wounded troops, and found them expressing ideas which inspired a later novel.

He was with US troops who entered the concentration camp of Buchenwald on April 14, 1945. His experience there would inform his research for and writing in the next decade of Andersonville, his novel about the Confederate prisoner of war camp. One of the issues he struggled with was how to think of the German civilians nearby. In his novel, he portrayed some civilian Southerners sympathetically, in contrast to officers at the camp.

When Kantor interviewed US troops, many told him the only goal was to get home alive. He was reminded of the Protestant hymn: "When all my labors and trials are o're / And I am safe on that beautiful shore [Heaven], O that will be / Glory for me!" Kantor returned from the European theater of war on military air transport (MAT). After the war, the producer Samuel Goldwyn commissioned him to write a screenplay about veterans' returning home. Kantor instead wrote a novel in blank verse, which was published as Glory for Me (1945). After selling the movie rights to his novel, Kantor was disappointed that the film was released under the name "The Best Years of Our Lives" (1946), and details of the story were changed by the screenwriter Robert Sherwood. Kantor was said to have lost his temper with Goldwyn and walked off the Hollywood lot. In the movie's first 15 seconds, it is identified as "based upon a novel by MacKinlay Kantor" but the novel's name was not told. His basic story had power, as the film was a commercial and critical success, winning seven Academy Awards.

Kantor also worked a police beat on newspapers, when he often rode with police on night shifts. These experiences inspired most of his short crime novels. Kantor was noted for his limited use of punctuation within his literary compositions..

In the November 22, 1960, issue of Look magazine, Kantor published a fictional account set as a history text, called If the South Had Won the Civil War. This generated such a response that it was published in 1961 as a book. It was the first of many alternate histories of that war.

In addition to journalism and novels, Kantor wrote the screenplay for the noted film noir motion picture Gun Crazy (aka Deadly Is the Female) (1950). He acted in the 1958 film Wind Across the Everglades.

Several of his novels were adapted for films. He established his own publishing house, and published several of his works in the 1930s and 1940s.

His last novel was Valley Forge (1975).

Kantor died of a heart attack in 1977, at the age of 73, at his home in Sarasota, Florida.

Novels

• Diversey (1928)
• El Goes South (1930)
• The Jaybird (1932)
• Long Remember (1934)
• The Voice of Bugle Ann (1935)
• Arouse and Beware (1936)
• The Romance of Rosy Ridge (1937)
• The Noise of Their Wings (1938)
• Here Lies Holly Springs (1938)
• Valedictory (Illustrated by Amos Sewell) (1939)
• Cuba Libre (1940)
• Gentle Annie (1942)
• Happy Land (1943)
• Glory for Me (1945)
• Midnight Lace (1948)
• The Good Family (1949)
• Wicked Water (1949)
• One Wild Oat (1950)
• Signal Thirty-Two (1950)
• Don't Touch Me (1951)
• Warwhoop: Two Short Novels of the Frontier (1952)
• The Daughter of Bugle Ann (1953)
• God and My Country (1954)
• Andersonville (1955)
• Frontier: Tales of the American Adventure (1959)
• The Unseen Witness (1959)
• Spirit Lake (1961)
• If the South Had Won the Civil War (1961) (Originally published in Look magazine, November 22, 1960)
• Beauty Beast (1968)
• I Love You, Irene (1973)
• The Children Sing (1974)
• Valley Forge (1975)

Collections

• Turkey in the Straw: A Book of American Ballads and Primitive Verse (1935)
• Author's Choice (stories) (1944)
• Silent Grow the Guns, and Other Tales of the American Civil War (stories) (1958)
• It's About Crime (stories) (1960)
• The Gun-Toter, and Other Stories of the Missouri Hills (stories) (1963)
• Story Teller (stories and essays) (1967)

Children's and young-adult books

• Angleworms on Toast (Illustrated by Kurt Wiese) (1942)
• Lee and Grant at Appomattox (Illustrated by Donald McKay) (1950)
• Gettysburg (Illustrated by Donald McKay) (1952)
• The Work of Saint Francis (Illustrated by Johannes Troyer) (1958)

Nonfiction

• But Look, the Morn: The Story of a Childhood (memoir) (1951)
• Lobo (1958)
• Mission with LeMay: My Story, by Curtis LeMay with MacKinlay Kantor (1965)
• The Day I Met a Lion (memoir/essays) (1968)
• Missouri Bittersweet (1969)
• Hamilton County (1970)

Films

• The Voice of Bugle Ann (novel) (1936)
• Mountain Music (story) (1937)
• The Man from Dakota (novel, Arouse and Beware) (1940)
• Happy Land (novel) (1943)
• Gentle Annie (novel) (1944)
• The Best Years of Our Lives (novel, Glory for Me) (1946)
• The Romance of Rosy Ridge (novel) (1947)
• Gun Crazy (story and screenplay) (1950)
• Hannah Lee: An American Primitive (novel, Wicked Water) (1953)
• Wind Across the Everglades (actor) (1958)
• Follow Me, Boys! (novel, God and My Country) (1966)

Television

• Lux Video Theatre, episode "Forever Walking Free" (story) (1951)
• Studio One in Hollywood, episode "Signal Thirty-Two" (novel) (1953)
• The 20th Century Fox Hour, episode "In Times Like These" (novel, Happy Land) (1956)