He received his B. A. from Pembroke Hall, Cambridge, in 1661 and his M. D. from the University of Leyden, in the Netherlands, in 1671.
Elected one of the early fellows of the Royal Society, he became its secretary in 1677.
Grew devoted long and continuous study to microscopic observation and, with Malpighi, was cofounder of the science of microscopic anatomy of plants.
Grew introduced the term "comparative anatomy" in his Comparative Anatomy of Trunks (1675).
He published Comparative Anatomy of the Stomach and Guts in 1681, a remarkable study based on research involving 35 species.
Grew showed an unusual grasp of relationships of the various organs of plants. He also observed and traced the vascular bundles of seedlings, and his The Anatomy of Vegetables was communicated to the Royal Society in 1670. Idea of a Phytological History appeared in 1672 and Anatomy of Plants in 1682.