Dienes was born in Transylvania, Austria-Hungary, on December 18, 1913, and left home at 15 after the suicide of his mother. Dienes travelld across Europe mostly on foot, until his arrival in Tunisia. In Tunisia he purchased his first camera, a 35mm Retina. Returning to Europe he arrived in Paris in 1933 to study art, and bought a Rolleiflex shortly after. Dienes began work as a professional photographer for the Communist newspaper L'Humanité, and was employed by the Associated Press until 1936, when the Parisian couturier Captain Molyneux noted his work and urged him to become a fashion photographer. In 1938 the editor of Esquire, Arnold Gingrich offered him work in New York City, and helped fund Dienes' passage to the United States. Once in the United States Dienes worked for Vogue andLife magazines as well as Esquire. When not working as a fashion photographer Dienes travelled the USA photographing Native American culture, including the Apache, Hopi, and Navajo reservations and their inhabitants. Dissatisfied with his life as a fashion photographer in New York, Dienes moved to California in 1944, where he began to specialise in nudes and landscapes.As well as Monroe, Dienes also photographed such notable actors as Elizabeth Taylor, Marlon Brando, Henry Fonda, Shirley Temple, Ingrid Bergman, Ronald Reagan, Jane Russell, Anita Ekberg and Fred Astaire. De Dienes married twice, and died of cancer on April 11, 1985.

In 1945 Dienes met the nineteen year old Marilyn Monroe, then called Norma Jean Baker, who was a model on the books of Emmeline Snively’s Blue Book Model Agency. Snively told Dienes of Norma Jean, and suggested her for his project of photographing artistic nudes. In his memoirs Dienes described the first time he met Monroe saying "...it was as if a miracle had happened to me. Norma Jean seemed to be like an angel. I could hardly believe it for a few moments. An earthly, sexy-looking angel! Sent expressly for me!" His series of pin-up shots of her at Long Island's Tobay Beach, in Oyster Bay, New York became notable. Norma Jean had recently separated from her husband, James Dougherty and told Dienes of her wish to become an actress. Dienes suggested that they go on a road trip to photograph her in the natural landscapes, for which Dienes paid her a flat fee of $200. Dienes had earlier been present at the first meeting of Monroe and her mother in six years, and had presumptuously announced to her mother that he and Monroe were to be married. His photographs of Monroe from this trip sold widely and he made far more money from the images, and did not offer Monroe a percentage of the sales, or paid her on the profits. Dienes next met her on Labor Day in 1946, with her new name of Marilyn Monroe, they next worked together in 1952, where he shot her at the Bel Air Hotel and 1953, where she telephoned him at 2am, and took him to a darkened street where he used his car headlights to illuminate her, taking pictures her wide-eyed and unmade up. Dienes last saw her alive in June 1961. Of their last meeting he said that "...her success was a sham, her hopes thwarted...the next day she left a bouquet outside my door: a selection of her latest photos. Smiling, radiant - utterly misleading; I little guessed that this was our last goodbye.”