The Some Like It Hot star was snapped by photographer Len Steckler as she visited poet Carl Sandburg in a New York apartment in December 1961.
The blonde bombshell is depicted wearing pointed glasses and a short-sleeved dress, while sipping whiskey and holding hands with the 83 year old.
Steckler tells Reuters, "It was serendipitous with these two icons in their moment and me here with my camera.
"I went to open the door and there I was face-to-face with Marilyn Monroe, and she looked more ravishing than on the screen. She said 'I am sorry I am late. I was at the hairdresser's, matching my hair to Carl's.'
"As we know, Marilyn loved older men, she loved the intellectuals and Carl was very parental with her. It was a lovely thing to see."
Monroe died in August 1962, while Sandburg passed away in 1967.
Steckler decided to sell the collection, entitled Marilyn Monroe: The Visit, after his son discovered the negatives.