An opponent of quarantine, he was recognised as an authority on epidemiology, and was employed in several government commissions of inspection and inquiry.
In 1849-50 he was a superintendent medical inspector of the General Board of Health; in 1852 he was sent by the Colonial Office to Jamaica, and wrote an official sanitary report.
He left a legacy of £2,000 to the college for the endowment of a lectureship on "state medicine and public health", and subjects connected with those.
He recommended the mitigation or total abolition of quarantine, and at the same time the dependence on sanitary measures alone for preservation from foreign pestilences.
[1] In 1862 Milroy was a member of a committee appointed by the College of Physicians at the request of the Colonial Office for the purpose of collecting information on the subject of leprosy.
Data were collected from the British Empire on the disease, which Milroy believed was "constitutional", and used selectively.
[2] The report was printed in 1867, and the appendix included Notes respecting the Leprosy of Scripture by Milroy.