Mansfield (Frederick W.) is born in East Boston.

The son of Irish immigrants, Frederick Mansfield graduates from East Boston High School and Boston University School of Law, becomes counsel for the state AFL labor union and president of the Massachusetts Bar Association, and counsel to the archdiocese of Boston. He lives at 15 Elm Hill Avenue. Mansfield serves as Massachusetts treasurer (1915), the first Democrat to hold the post, is an unsuccessful candidate for governor in 1916 and 1917, and an unsuccessful candidate for mayor several times, before serving as mayor of Boston (1934-37). He dies on November 6, 1958, and is buried in Holyhood Cemetery in Brookline.