While a student, Paul wrote and published A Catalogue of the Flowering Plants and Ferns growing in the neighbourhood of Aberdeen, with the help and support of his father.
He gained his MA in 1851,[1] but when his father died in September 1852, MacGillivray lost interest in science, and instead chose to study medicine in London; in 1855 he was elected a member of the Royal College of Surgeons.
He joined the Field Naturalists' Club of Victoria and gained a reputation as an observer, describing novel species of plumatella[3] and studying the unique polyzoa of Australia, collected by the South Australian Museum and the "indefatigable" J. Bracebridge Wilson" around Port Phillip Heads.
MacGillivray had not completed a promised chapter on zoophytes and fossils for Sir Frederick McCoy's projected A Natural History of Australia,[5] and was close to completing a monograph (on the Polyzoa of Victoria) for the Royal Society of Victoria, when he died on 9 July 1895 at his house on Forest Street, Bendigo.
[6] His collections, papers, findings and library were donated to the National Museum of Victoria by the government shortly after his death.