Willis was self-educated at Harrow School in 1937-1942. He had two oil paintings hung in the summer exhibition of the Royal Academy at Burlington House in 1941. Willis joined the RNVR in 1942 and served in Destroyers and Combined Operations, landing American tanks on Utah Beach on Normandy D-Day, where he was wounded. After a pleasant time recovering and painting, Willis was posted to Italy. As a painter and lover of Nelson's Navy, he considered himself privileged to be posted for a time to the flagship, HMS Victory in Portsmouth, where, as a humble Ordinary Seaman, he managed to get permission to paint in the Great Cabin. Willis returned to civilian life in 1946 and studied Art at the University of Reading under Professor Betts. It was during his time in Reading that Willis met Diana Bateman, elder daughter of the cartoonist H.M. Bateman. He married Diana in 1948 and they have two sons and two daughters, all living near them in Somerset. Both daughters are successful artists.