Two years after his father's death Gregory was admitted a queen's scholar of Westminster School, from which in 1714 he was elected to Christ Church, Oxford.
He continued to hold his professorship till 1736, when he resigned it on his appointment to a canonry in Christ Church Cathedral (installed 8 June).
Under his directions while dean the upper rooms in the college library were finished (1761), and he is said to have restored the terraces in the great quadrangle (Tom Quad).
On 15 September 1759 he was also appointed Master of Sherburn Hospital, County Durham, where he started to cut down a wood on the hospital estates, and with the proceeds from the timber improved the accommodation, as mentioned by an anonymous eulogy Essay on the Life of David Gregory, late Dean of Christ Church, London (1769).
He died at the age of seventy-one, 16 September 1767, and was buried under a plain slab with a short Latin inscription in the cathedral, his wedding ring tied to his finger.