William James Sinnott (sometimes mistakenly listed as Arthur Sinnott) was born in Boston in 1875. He studied at the Museum of Fine Arts in Boston and began his career as an odd-jobs artist, later working on the staffs of various Boston newspapers, such as the Globe, Herald-Traveler, and the Journal. He created several comic strips, like 'Vivian and Viola', which appeared from about 1900 to 1910, and 'Dicky Dippy's Diary', which was published from about 1910 to 1927. The latter was sold in syndication to a hundred other newspapers in the US and Canada. Other strips by Sinnott were 'Mildred Didn't Mean To', 'Viola' and 'Victor and Velvet' (1912).
In the 1920s, he gave up newspaper work to become advertising manager of Raymond's Department Store (which no longer exists but was very prominent in Boston in the first half of the 20th century). At Raymond's, he created advertisements in the form of elaborate cartoons, and they frequently filled a half page in the Boston Globe. Eight or nine of them are reproduced in the book 'Hayseed ans Sawdust: The Story of Raymond's' by Frank I. Dorr (Boston, 1934). Dorr was the head of Raymond's for many years.
William J. Sinnott lived in Dorchester, Massachusetts until his death in 1933.