With birthplace unknown, William Jennys, an itinerant portrait painter, was painting portraits in the vicinity of New Milford, Connecticut in the mid1790s, then New York City, and after 1800 in the Connecticut River Valley into Massachusetts, Vermont, New Hampshire and the southern states. It appears that his career began in 1792, when he first advertised in Norwich, Connecticut as a portrait painter. However, "the sedentary life did not suit the independent artist, and he soon became an intinerant painter, traveling throughtout New England and New York."
He trained with his father, Richard Jennys, and they traveled together, but William's style was more realistic than his father's and showed "greater attention to the modeling of facial features and the depcition of his sitters' unique personalities." But he was unskilled with arms and legs and usually avoided showing them. Jennys was financially successful, and in 1804 settled in Newburyport, Massachusetts where, during the next five years he had the most productive period of his career, completing thirtyfive portraits. After 1817, he moved to Littleton, New Hampshire with his wife until his death in 1859.
The portraits of William Jennys with their strong, pictorial style and appearance of direct light combined with shadow influenced other Connecticut artists such as Simon Fitch and Reuben Moulthrop.