John Bartholomew Callan KC (15 August 1882 – 12 February 1951) was a New Zealand judge.

[9] As a Judge, apart from the normal case load, Justice Callan also undertook Government investigations on the Aliens Tribunal and on the leakage of information (both relevant to World War II).

Apart from his ten years as Dean of the Faculty of Law at the University of Otago (1924–34), he was also a member of the Council of Legal Education.

His favourite leisure occupation seemed to be the recital in detail of matters grave or gay in some case with which he had been concerned either as counsel or Judge."

In 1922, (while still practising in Dunedin) Callan provided legal advice to Liston when the latter was charged with sedition.

[11] When Pope Pius XII stated that Catholic judges should not play any part in divorce cases, a disturbed Callan indicated that he was prepared to resign but decided, after discussion with Liston, that the Pope's statement did not apply to New Zealand as "divorce could be understood to refer to the civil contract of marriage rather than to the sacrament of matrimony".

[2] In spite of this decision, Callan remained a close friend of Liston until his death.