[2] The Jewish family moved to Berlin, Germany, in 1929; when the Nazis came to power in 1933, they fled persecution to Milan in 1933.
[2] After graduation from college, Gruen moved back to New York City where he settled in Greenwich Village.
[2] He took jobs as a book buyer at Brentano's, a publicity director at Grove Press and a photographers' agent.
[2] He became friends with composer Virgil Thomson which inspired Gruen to contribute music reviews to the New York Herald Tribune, later becoming part of its staff in addition to acting as the paper's art critic.
Gruen captured images of the creative icons in his social and professional circles including Yoko Ono, Jasper Johns, Larry Rivers, Leonard Bernstein and Willem de Kooning.
[2] Many of those photographs were later acquired by the Whitney Museum of American Art and presented in a 2010 exhibition, "Facing the Artist: Portraits by John Jonas Gruen".