Mary Kim was a Human school teacher who lived in South Carolina, on Earth. She was married to John Kim and the two had a single son, Harry, who was born in 2349. John and Mary Kim considered Harry to be their "miracle child", as they had trouble conceiving. (VOY: "Eye of the Needle", "Favorite Son")

In 2358, the Kims participated in a humanitarian mission to a colony that had just suffered from a radiation disaster. (VOY: "The Thaw")

Just before the USS Voyager left Earth in 2371, Mary contacted Captain Janeway to ask if she had time to send Harry's clarinet, which he had left behind. The captain had to tell her no, as they were due at Deep Space 9. (VOY: "Caretaker")

Harry Kim had a flashback of his mother in 2373 that was induced by the Taresians. (VOY: "Favorite Son")

On her birthday in 2378, she finally got the chance to speak to him face-to-face for the first time in seven years. During the conversation she stated that Harry was very popular with her 8th graders. She was hoping he could record a short presentation about what it is like to command a starship. (VOY: "Author, Author")