Born in Penns Grove, New Jersey, Hennings was reared in Chicago,He graduated with honors in 1904 from the Art Institute of Chicago, then studied briefly at the Pennsylvania Academy of the Fine Arts, Philadelphia. Between 1912 and 1915 he studied in Munich under Franz von Stuck, Walter Thor, and Angelo Junk, and spent a period at the Royal Bavarian Academy.After a few months in Glouster, Massachusetts, Hennings settled in Chicago, where in 1915 he taught at the Chicago Academy of Fine Arts and worked in a commercial studio painting murals. On a subsidy furnished by Chicago patrons, he painted in Taos but spent a few months each year in Chicago until the early 1930s. Hennings painted in North Africa and southern France in 1926. In the late 1930s, he resided a few months each year in Houston, returning to Taos in the early spring. Noted for his paintings of American Indians, a year before his death he was commissioned by the Santa Fe Railway to do several paintings on the Navajo Reservation.He died in Taos of a heart attack.