Under J. K. Adey's supervision at Sunbury, Ellery developed a greater understanding of psychiatry; together they were responsible in 1925 for the first successful application in Australia of Wagner-Jauregg's malarial-fever treatment for general paralysis of the insane.
A member of the British Psychological Society, from 1938 Ellery allied himself with a group of progressive psychiatrists led by Dr Paul Dane.
In establishing the Melbourne Institute for Psycho-Analysis in October 1940, the group encountered opposition from both the Federal government and the local branch of the British Medical Association.
Throughout his career, he continued to lobby for the rights of psychiatric patients, socialised medicine and for a more progressive understanding of the psychological nature of crime.
He wrote articles for the Angry Penguins journal and spoke for the defence of Max Harris at the Ern Malley pornography trial.