Ennis is a portrait painter and former book-cover illustrator; his paintings currently hang in over 100 fine art collections worldwide.

In 1997, he authored the book Going Digital, An Artist's Guide to Computer Illustration published by Madison Square Press.

He went on to paint several hundred private and institutional portraits winning numerous national awards.

His portrait subjects include Penn Medicine CEO Ralph Muller, Superintendent of the United States Naval Academy Vice Admiral John R. Ryan, FAA Administrator Randy Babbitt, oncologist Dr. Stephen Hahn, NIEHS Director Dr. Linda Silber Birnbaum, M.I.T.

Nobel Laureate Susumu Tonegawa, notable corporate leaders Al McNeill of Turner Corporation, and John Bryson of Southern California Edison, noted philanthropists William and Joan Schreyer, the first woman headmaster of Boston Latin School, Cornelia Kelley, and the first African American Dean of University of South Carolina Law School, Burnele Powell.