Marion was born in Halifax in 1913. She attended Alexandra School and later Mount St. Vincent University followed by a year at Dalhousie University. Over this time, she acquired training in bookkeeping. During the Second World War, Marion, and her sister, Louise, became Red Cross volunteer workers. Marion was also a member of the Izaak Walton Children's Hospital Auxiliary for many years.

In 1942, Marion, together with Louise and Sam Goodman (her brother-in-law), became one of the three trustees of her Great Aunt Rebecca Cohn's estate. Rebecca Cohn had stipulated in her will that the assets were to be held for twenty years before being distributed to charities.

During this period, the assets grew in value and Marion began her education in the art of charitable giving. The most notable result was the gift of the Rebecca Cohn Auditorium to Dalhousie University, reflecting the Keshen family's interest in music. The trustees also made donations to St. Mary's University, the Boy Scouts and the Girls Guides of Nova Scotia and other local charities. Marion Keshen continued to administer the trust until her death in 1992.

As a regular user of the Library she made a number of donations to the Halifax Library. Contributions ranged from art books, which were too expensive for the library budget, to a fine magnifying glass for the reference room of the Spring Garden Road Library that enabled the visually impaired to use dictionaires and other reference materials in the reference room.

It is not surprising that Marion Keshen gave the Halifax Library a major bequest upon her death -thus, returning to the community much that the City in which she had been born and raised had given to her family and herself.