After the death of Johann Jacob Dillenius (1684–1747), he became the Sherardian Professor of Botany at the University of Oxford from 1747 to 1783.
He began the catalogue of the plants of the botanical garden of the university, Catalogus Plantarum Horti Botanici Oxoniensis.
His youngest son was the botanist John Sibthorp (1758–1796), who continued the Catalogus Plantarum.
8 Jul 1743 - d. 9 Sep 1843) and was the mother of Sir Montague Cholmeley, 1st Baronet.
Another daughter Mary Elizabeth was the second wife of Sir Thomas Sewell, Master of the Rolls.