Mary Morstan is Watson’s only canonically named wife. She is the daughter of Captain Arthur Morstan, an Indian Army officer. After her mother died Mary was sent to Edinburgh, where she lived in a boarding establishment. She and Watson met when she sought Holmes’s aid in The Sign of Four. At the time, Miss Morstan was a governess in the employ of a Mrs. Cecil Forrester.
Watson describes her as “a blonde young lady, small, dainty, well gloved, and dressed in the most perfect taste…Her face had neither regularity of feature nor beauty of complexion, but her expression was sweet and amiable, and her large blue eyes were singularly spiritual and sympathetic…. I have never looked upon a face which gave a clearer promise of a refined and sensitive nature.” Holmes was also taken with her, for different reasons: “I think she is one of the most charming young ladies I ever met and might have been most useful in such work as we have been doing.”
Speaking of their work, Watson’s wife is presented as supportive of the doctor’s continued participation in Holmes’s cases. She likely felt some fondness and gratitude toward the detective for introducing her to Watson (not to mention solving the mystery of her father’s disappearance). On the other hand, she may have seen Holmes as a rival for her husband’s attention. However, as Watson reports that “after my marriage…these occasions grew more and more seldom, until I find that in the year 1890 there were only three cases of which I retain any record” (FINA), it would appear that he had made his domestic and professional obligations his highest priorities.
Mrs. Watson appears to have died during the Great Hiatus, as Watson states in “The Adventure of the Empty House” that Holmes “had learned of my own sad bereavement.”