Born to Henry and Sarah (Malony) Pennington, in Nashville, Tennessee. Her Quaker upbringing emphasized education, self-reliance, and social justice.

Pennington dedicated herself to her scientific career and did not marry. This was a common choice for women pursuing professional careers in the early 20th century, as societal expectations often made it difficult to balance marriage and career aspirations.

Pennington fostered strong professional networks with fellow scientists, government officials, and industry leaders. She collaborated with many individuals throughout her career, building lasting relationships based on shared goals and mutual respect. Her relationships included interactions and collaborations with scientists at the USDA and within the Refrigeration industry

It is likely Pennington informally mentored younger scientists, particularly women, in fields related to food science and safety. As a pioneering woman in STEM, she likely served as a role model and inspiration for others entering male-dominated fields.

Mary Engle Pennington died on December 27, 1952. Her personal legacy is one of fierce independence, unwavering commitment to scientific advancement, and profound impact on food safety and public health. Details about her later years and close personal relationships remain limited within easily available historical sources.