Gregory, the grandson of James Gregory, was born in Aberdeen, Scotland to the professor of medicine James Gregorie and Anna Chalmers, his father’s second wife.
Gregory’s father died when he was eight years old.
From then on Principal Chalmers, his grandfather, and his half-brother James, a professor of medicine, took over his education.
His cousin Thomas Reid, the moral philosopher, also guided and influenced his education.
Gregory attended a local grammar school and later King’s College, University of Aberdeen.
In 1742 he and his mother moved to Edinburgh where he studied medicine.
There he became friends with the physician and poet Mark Akenside.
Gregory went to Leiden to continue his studies in 1745.
In 1746, soon after receiving his degree, he was appointed professor of philosophy at King’s College.
He taught mathematics and moral and natural philosophy.
He was also a practicing doctor and preferring patients to lecturing, he resigned his academic post in 1749.
On 2 April 1752, Gregory married Elizabeth Forbes.
Together they had three sons, including the physician James Gregory, and three daughters.
In 1754 the family moved to London and they entered the social circle of John Wilkes, Charles Townshend, George Lyttelton and Elizabeth Montagu.
It was at this time that he started spelling his name ˝Gregory˝ rather than ˝Gregorie˝.
In 1756 he was elected a fellow of the Royal Society.
Gregory subsequently returned to Aberdeen to take up another academic post.
While at Aberdeen, Gregory attempted to institute a series of medical lectures, but there were too few medical students to sustain them.
He also became an active member of Aberdeen Philosophical Society which he had co-founded with 5 others including Prof Robert Trail.
The paper he presented there were later collected and published anonymously in A Comparative View of the State and Faculties of Man, with those of the Animal World (1765).
Gregory believed in a universal human nature that could be discovered through scientific experiment.
The most important elements of human nature, as he saw it, were reason and instinct.
He wrote that ˝the task of improving our nature, of improving man’s estate, involves the proper development and exercise of the social principle and the other principle of instinct, with reason subordinate to instinct and serving as a corrective on it˝.
Studying the natural world leads to a cultivation of good taste and religious understanding for Gregory.