[1] In February 1873 MacGregor became assistant medical officer at the Seychelles, and in 1874 he was appointed resident at the hospital and superintendent of the lunatic asylum at Mauritius.

Doctor MacGregor organised a relief expedition and personally saved several lives; his report made no mention of his own deeds, but they could not remain hidden, and he was given the Albert Medal, and the Clarke gold medal of the Royal Humane Society of Australasia for saving life at sea.

[4] MacGregor's experience with native races led to his being appointed administrator of British New Guinea, from 4 September 1888 to 13 March 1895.

It was necessary at times to make punitive expeditions, but bloodshed was avoided as much as possible, and by tact and perseverance MacGregor eventually brought about a state of law and order.

Some of this in part related to the annual headhunting raid and cannibalisation of coastal tribes by the Tugeri warriors, which he ended.

In 1892 the position was sufficiently settled to enable him to publish a Handbook of Information for intending Settlers in British New Guinea.

[5] From 1899 to 1904 he was governor of Lagos Colony, Nigeria, where he instituted a campaign against the prevalent malaria, draining the swamps and destroying as far as possible the mosquitoes which were responsible for the spread of the disease.

His efforts to improve the health of his community led to his being given the Mary Kingsley Medal in 1910 by the Liverpool School of Tropical Medicine.

He also did valuable work in dealing with the fisheries question, persuading the contending parties to refer the dispute to the Hague international tribunal which brought about an amicable settlement.

[8] MacGregor assisted in the inauguration of the University of Queensland, he agreed to the handing over of his residence Old Government House to be its first home, and one of his first acts as governor was to attend the dedication ceremony on 10 December 1909.

In 1914 MacGregor retired and went to live on the estate 'Chapel-on-Leader'[23] (near the River Leader, half-way between Lauder and Earlston, Berwickshire, Scotland).

[24] After an operation for intestinal adhesions and gallstones MacGregor died on 3 July 1919,[2] was cremated,[23] and interred beside his parents in the churchyard of Towie,[1] the village where he was born.

[23] In earlier years from his Papuan times, ethnological specimens were collected and presented to the Queensland Museum, bird specimens to the museum in Sydney, and a collection of flora to the botanical department in Melbourne; the latter indicated to have made the botanist Baron Von Mueller 'wildly enthusiastic'.