Winsor (Justin) is born in Boston.

Justin Winsor graduates from Boston Latin School and Harvard College, then studies in Europe. Returning to Boston, he works initially as a freelance writer and moved to 61 West Newton Street in the early 1860s. Winsor serves as superintendent of the Boston Public Library (1868-1877) and is credited with professionalizing the library. He resigns amid a controversy in 1877,* and immediately becomes Librarian of Harvard University. Winsor edits the most comprehensive history of Boston, which is published in 1880.* He dies in Cambridge on October 22, 1897.