His senior officer at Portsmouth was Thomas Mott Osborne, a penologist who later employed MacCormick.
When he retired from teaching at Berkeley, MacCormick worked full time as the executive director of the Osborne Association until his death in 1979.
In 1971, MacCormick served as co-chairman of the Goldman Panel, which was charge with conducting an impartial investigation of how Attica Prison inmates were being treated after the retaking of the facility following the uprising at the prison that resulted in a massacre of inmates and hostages by New York state troopers.
He served on committees concerned with alcoholism and drug use and wrote many papers expressing progressive ideas on prison reform, libraries, and juvenile delinquency.
[1] MacCormick wrote a book based on the results of his 1928 nationwide survey of prison education, which was published in 1931 as The Education of Adult Prisoners: A Survey and a Program Prepared for the National Society of Penal Information.