She eventually moved on to join the staff of N. H. Miller & Company, an advertising agency, where she rose to the level of vice president; she retired in 1982.
[1] While continuing to work at the advertising company during the day, MacLeod began writing mystery fiction, eventually publishing over 30 novels.
Many of her books are set in New England, including a series featuring university professor Peter Shandy, and another about Beacon Hill couple Sarah Kelling and Max Bittersohn.
MacLeod tailored her books to fit into the cozy mystery genre, i.e. avoiding too much violence, gore, or sex while featuring a humorous and literate-yet-light style, likable protagonists, and eccentric casts of secondary characters.
Although described as a "true lady" and often seen with hat and white gloves, while writing she would stay dressed in a bathrobe to avoid the temptation of leaving the house for an errand.