After attendance in the local schools, where he his prime enthusiasm was the theater, Koch entered the University of Minnesota, studying comparative literature.

At City College, he was awarded what he still regards as the greatest honor of his life, when he was named the most promising future law student in his graduating class.

In 1969, he completed his first novel, Night Watch, which was published by Harper and Row to generally strong positive critical response both in print and the media.

After that, he became a regular contributor to various magazines, notably Harper's and Esquire, where during the first wave of feminism, he published a widely noticed essay "The Guilty Sex".

His relation with Harper’s Magazine ended when the editor refused to publish his enthusiastic essay about Robert Wilson and Philip Glass’ avant-garde opera Einstein on the Beach.

Later, because of his longstanding interest in the forces that led to German fascism and the Second World War, he published Hitler's Pawn: The Boy Assassin and the Holocaust, the story of the obscure Jewish teenager in Paris whose assassination of a German diplomat was used by Hitler as a pretext for Kristallnacht, a turning point in the Nazis' persecution of the Jews and prelude to the Holocaust.

Shortly before he died from AIDS-related complications in 1987, photographer Peter Hujar named Koch as the executor of his artistic estate.

[7][8][9] In 2017, a retrospective of Hujar's work, curated at the Morgan Library & Museum in New York, travelled to major venues in the United States and Europe.